Synthetic oplophorus luciferases with enhanced light output

ABSTRACT

A polynucleotide encoding a modified luciferase polypeptide. The modified luciferase polypeptide has at least 60% amino acid sequence identity to a wild-type  Oplophorus  luciferase and includes at least one amino acid substitution at a position corresponding to an amino acid in a wild-type  Oplophorus  luciferase of SEQ ID NO:1. The modified luciferase polypeptide has at least one of enhanced luminescence, enhanced signal stability, and enhanced protein stability relative to the wild-type  Oplophorus  luciferase.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/053,252, filed Oct. 14, 2013, now allowed, which is a continuation ofU.S. patent application Ser. No. 12/773,002, filed May 3, 2010, now U.S.Pat. No. 8,557,970, which claims priority to United States ProvisionalApplication No. 61/174,838, filed May 1, 2009, each of which isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to synthetic Oplophorus luciferases havingenhanced properties compared to wild-type Oplophorus luciferase.

The deep-sea shrimp Oplophorus gracilirostris ejects a blue luminouscloud from the base of its antennae when stimulated, like various otherluminescent decapod shrimps including those of the genera Heterocarpus,Systellaspis and Acanthephyra (Herring, J. Mar. Biol. Assoc. UK,156:1029 (1976)). The mechanism underlying the luminescence ofOplophorus involves the oxidation of Oplophorus luciferin(coelenterazine) with molecular oxygen, which is catalyzed by Oplophorusluciferase as follows:

Coelenterazine, an imidazopyrazinone compound, is involved in thebioluminescence of a wide variety of organisms as a luciferin or as thefunctional moiety of photoproteins. For example, the luciferin of thesea pansy Renilla is coelenterazine (Inoue et al., Tetrahed. Lett.,18:2685 (1977)), and the calcium-sensitive photoprotein aequorin fromthe jellyfish Aequorea also contains coelenterazine as its functionalmoiety (Shimomura et al., Biochem., 17:994 (1978); Head et al., Nature,405:372 (2000)).

SUMMARY

In one embodiment, the invention provides a polynucleotide encoding amodified luciferase polypeptide. The modified luciferase polypeptide hasat least 60% amino acid sequence identity to a wild-type Oplophorusluciferase and includes at least one amino acid substitution at aposition corresponding to an amino acid in a wild-type Oplophorusluciferase of SEQ ID NO:1. The modified luciferase polypeptide has atleast one of enhanced luminescence, enhanced signal stability, andenhanced protein stability relative to the wild-type Oplophorusluciferase.

In another embodiment, invention provides a polynucleotide encoding fora modified luciferase polypeptide. The modified luciferase polypeptidehas enhanced luminescence relative to the wild-type Oplophorusluciferase and a substitution of at least one amino acid at position 2,4, 11, 20, 23, 28, 33, 34, 44, 45, 51, 54, 68, 72, 75, 76, 77, 89, 90,92, 99, 104, 115, 124, 135, 138, 139, 143, 144, 164, 166, 167, or 169corresponding to SEQ ID NO:.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows secondary structure alignments of fatty acid bindingproteins (FABPs) and OgLuc.

FIG. 2 shows secondary structure alignments of dinoflagellateluciferase, FABP and OgLuc.

FIG. 3 shows an alignment of the amino acid sequences of OgLuc andvarious FABPs (SEQ ID NOs: 1, 3, 4, 5, and 17-20, respectively) based on3D structure superimposition of FABPs.

FIGS. 4A-D shows the light output (i.e. luminescence) time course ofOgLuc variants modified with a combination of two or more amino acidsubstitutions in OgLuc compared with the N166R OgLuc variant and Renillaluciferase. 4A-4B) Luminescence (“lum”) in relative light units (RLU)using a “Flash” luminescence assay shown on two different luminescencescales over time in minutes. 4C-4D) Luminescence (“lum”) in RLU using a“Glo” 0.5% tergitol luminescence assay shown on two differentluminescence scales over time in minutes.

FIGS. 5A-C summarize the average luminescence in RLU of the variousOgLuc variants described in Example 7 (“Sample”) at T=0 (“Average”),with standard deviation (“Stdev”) and coefficient of variance (“CV”)compared with WT OgLuc, using a 0.5% tergitol assay buffer.

FIGS. 6A-B summarize the increase fold in luminescence at T=0 of theOgLuc variants over WT OgLuc determined from the 0.5% tergitol assaybuffer data shown in FIGS. 5A-C.

FIGS. 7A-C summarize the average luminescence in RLU of the OgLucvariants (“Sample”) at T=0 (“Average”), with standard deviation(“Stdev”) and coefficient of variance (“CV”) compared with WT OgLuc,using RLAB.

FIG. 8 summarizes the increase fold in luminescence at T=0 of the OgLucvariants over WT OgLuc determined from the RLAB data shown in FIGS.7A-C.

FIGS. 9A-D shows the signal stability of the OgLuc variants compared toWT OgLuc, using a 0.5% tergitol assay buffer. 9A-9C) Light output timecourse of the OgLuc variants (“clone”), with luminescence measured inRLU over time in minutes. 9D) Signal half-life in minutes of the OgLucvariants determined from light output time course data shown in FIGS.9A-C.

FIGS. 10A-C shows the light output time course (i.e. signal stability)of the OgLuc variants compared to WT OgLuc, using RLAB, withluminescence measured in RLU over time in minutes.

FIGS. 11A-B shows the signal half-life in minutes of the OgLuc variantscompared to WT OgLuc determined from light output time course data shownin FIGS. 10A-C.

FIGS. 12A-B shows the protein stability at 22° C. as the half-life inminutes of the OgLuc variants compared to WT OgLuc.

FIGS. 13A-B summarize the average luminescence in RLU of the A33K andF68Y OgLuc variants at T=0 (“Average”), with coefficient of variance (“%cv”), compared to WT OgLuc, using 0.5% tergitol assay buffer (13A) orRLAB (13B).

FIGS. 14A-B summarize the increase fold in luminescence at T=0 of theA33K and F68Y OgLuc variants over WT OgLuc, determined from the datashown in FIGS. 13A-B for assays using 0.5% tergitol assay buffer (14A)or RLAB (14B), respectively.

FIGS. 15A-B shows the signal stability of the A33K and F68Y OgLucvariants compared to WT OgLuc, using 0.5% tergitol assay buffer. 15A)Light output time course of the A33K and F68Y OgLuc variants, withluminescence measured in RLU over time in minutes. 15B) Signal half-lifein minutes of the A33K and F68Y OgLuc variants determined from lightoutput time course data shown in FIGS. 15A.

FIGS. 16A-B shows the signal stability of the A33K and F68Y OgLucvariants compared to WT OgLuc using RLAB. 16A) Light output time courseof the A33K and F68Y OgLuc variants, with luminescence measured in RLUover time in minutes. 16B) Signal half-life in minutes of the A33K andF68Y OgLuc variants determined from light output time course data shownin FIGS. 16A.

FIG. 17 shows the protein stability at 22° C. as the half-life inminutes of the A33K and F68Y OgLuc variants.

FIGS. 18A-B show the light output time course (i.e. signal stability) ofthe Core Combination OgLuc variants compared to the N166R OgLuc variantand Renilla luciferase, using 0.5% tergitol assay buffer, withluminescence measured in RLU over time in minutes.

FIG. 19 shows the light output time course (i.e. signal stability) ofthe Core Combination OgLuc variants compared to the N166R OgLuc variantand Renilla luciferase, using RLAB, with luminescence measured in RLUover time in minutes.

FIGS. 20A-B shows the light output time course (i.e. signal stability)of the C1+C2+A4E and C1+A4E OgLuc variants compared to WT OgLuc(“Og-Luc”) and Renilla luciferase (“hRL”), and the T2T and A54Fvariants, using 0.5% tergitol assay buffer (20A) or RLAB (20B), withluminescence measured in RLU over time in minutes.

FIG. 21 shows the light output time course (i.e. signal stability) ofthe C1+C2+A4E and C1+A4E OgLuc variants compared to WT OgLuc (“Og-Luc”)and Renilla luciferase (“hRL”) and the T2T and A54F variants, using0.25% tergitol assay buffer, with luminescence measured in RLU over timein minutes.

FIG. 22 shows the light output time course (i.e. signal stability) ofthe C1+C2+A4E and C1+A4E OgLuc variants compared to WT OgLuc (“Og-Luc”)and Renilla luciferase (“hRL”) and the T2T and A54F variants, in HEK 293cells with RLAB buffer, normalized to firefly.

FIG. 23 shows the light output time course (i.e. signal stability) ofthe C1+C2+A4E and C1+A4E OgLuc variants compared to WT OgLuc (“Og-Luc”)and Renilla luciferase (“hRL”), in HEK 293 cells, using 0.25% tergitolbuffer, normalized to firefly.

FIG. 24 shows the shows the protein stability as the half-life inminutes of the C1, C1+A4E, C1+C2+A4E, and C1+C3+A4E OgLuc variantscompared to WT OgLuc, Renilla luciferase and the N166R variant atvarious temperatures, such as 22, 37, 42, 50 and 54° C.

FIG. 25 shows the light output time course (i.e. signal stability) ofthe C1, C1+A4E, C1+C2+A4E, and C1+C3+A4E OgLuc variants compared to WTOgLuc (“Og-Luc”) and Renilla luciferase (“hRL”), using RLAB withluminescence measured in RLU (“lum”) over time in minutes, and thehalf-life in minutes determined from the time course data.

FIG. 26 shows the optimal wavelength in nm with the greatestluminescence, using coelenterazine as substrate for N166R, C1+A4E andC1+C2+A4E variants compared to Renilla luciferase, normalized by thehighest RLU value in the spectrum.

FIGS. 27A-B summarize the increase fold in luminescence at T=0 of therandomly mutagenized variants of C1+A4E (“sample ID”) over thecorresponding starting C1+A4E variant with the amino acid changeindicated, using 0.5% tergitol buffer.

FIG. 28 summarizes the increase fold in luminescence at T=0 of the L92variants of C1+A4E over the corresponding starting C1+A4E variant withthe amino acid change indicated, using 0.5% tergitol buffer.

FIG. 29 summarizes the increase fold in luminescence at T=0 of thecombination variants of C1+A4E (“Sample ID”) over the correspondingstarting C1+A4E variant with the amino acid changes indicated, using0.5% tergitol buffer.

FIG. 30 shows the light output time course of the natural logarithm (ln)value of luminescence measured in RLU over time in minutes and thehalf-life in minutes of the variant C1+A4E+F54I, compared tocorresponding starting C1+A4E OgLuc at 50° C.

FIG. 31 shows the amino acid sequence alignment of SEQ ID NO:10(NATIVE), SEQ ID NO:13 (Synthetic WT), SEQ ID NO:15 (N166R), SEQ IDNO:25 (C1), SEQ ID NO:27 (C1+C2), SEQ ID NO:23 (C1+A4E), SEQ ID NO:29(C1+C2+A4E), and SEQ ID NO:31 (C1+C3+A4E) with the consensus sequence.

FIG. 32 shows the nucleotide sequence alignment of SEQ ID NO:12(NATIVE), SEQ ID NO:2 (Synthetic WT), SEQ ID NO:14 (N166R), SEQ ID NO:18(C1), SEQ ID NO:20 (C1+C2), SEQ ID NO:16 (C1+A4E), SEQ ID NO:22(C1+C2+A4E), and SEQ ID NO: 24 (C1+C3+A4E) with the consensus sequence.

FIG. 33A summarizes the increase fold in luminescence at T=0 of theOgLuc variants over N166R determined from the 0.5% tergitol assay bufferdata shown in FIGS. 5A-C and 14A, normalized to the N166R variant.

FIG. 33B summarizes the increase fold in luminescence at T=0 of theOgLuc variants over N166R determined from the RLAB data shown in FIGS.7A-C and 14B, normalized to the N166R variant.

FIG. 33C summarizes the signal half-life in minutes of the OgLucvariants determined from the light output time course data shown inFIGS. 9A-C and 15B (0.5% tergitol assay buffer) and 10A-C and 16B (RLAB)normalized to the N166R variant.

FIG. 33D summarizes the protein stability at 22° C. as the half-life inminutes of the OgLuc variants compared to WT OgLuc shown in FIGS. 12A-Band 17 normalized to the N166R variant.

FIG. 33E summarizes the increase fold in luminescence, signal half-lifeand half-life at 22° C. shown in FIGS. 33A-D.

FIG. 34A shows the luminescence results of E. coli lysates containingthe IV variant (“IV”), Renailla luciferase (“Renilla”) and C1+A4E(“C1A4E”) assayed with 0.5% tergitol.

FIG. 34B shows the protein stability at 50° C. as the half-life inminutes of the VI variant (“VI”) and Renilla luciferase (“Renilla”).

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of structure, synthesis, and arrangement of components setforth in the following description or illustrated in the followingdrawings. The invention is described with respect to specificembodiments and techniques, however, the invention is capable of otherembodiments and of being practiced or of being carried out in variousways.

In the following description of the methods of the invention, processsteps are carried out at room temperature (about 22° C.) and atmosphericpressure unless otherwise specified. It also is specifically understoodthat any numerical range recited herein includes all values from thelower value to the upper value. For example, if a concentration range orbeneficial effect range is stated as 1% to 50%, it is intended thatvalues such as 2% to 40%, 10% to 30%, or 1% to 3%, etc. are expresslyenumerated in this specification. Similarly, if a sequence identityrange is given as between, e.g., 60% to <100%, it is intended that 65%,75%, 90%, etc. are expressly enumerated in this specification. These areonly examples of what is specifically intended, and all possiblenumerical values from the lowest value to the highest value areconsidered expressly stated in the application.

In embodiments of the present invention, various techniques as describedherein were used to identify sites for amino acid substitution toproduce an improved synthetic Oplophorus luciferase polypeptide.Additional techniques were used to optimize codons of thepolynucleotides encoding for the various polypeptides in order toenhance expression of the polypeptides. It was found that making one ormore amino acid substitutions, either alone or in various combinations,produced synthetic Oplophorus-type luciferases having at least one ofenhanced luminescence, enhanced signal stability, and enhanced proteinstability. Furthermore, including one or more codon optimizingsubstitutions in the polynucleotides which encode for the variouspolypeptides produced enhanced expression of the polypeptides in variouseukaryotic and prokaryotic expression systems.

Luminescence refers to the light output of the luciferase polypeptideunder appropriate conditions, e.g. in the presence of a suitablesubstrate such as a coelenterazine. The light output may be measured asan instantaneous or near-instantaneous measure of light output (which issometimes referred to as “T=0” luminescence or “flash”) upon start ofthe luminescence reaction, which may start upon addition of thecoelenterazine substrate. The luminescence reaction in variousembodiments is carried out in a solution containing lysate, for examplefrom the cells in a prokaryotic or eukaryotic expression system; inother embodiments, expression occurs in an in vitro system or theluciferase protein is secreted into an extracellular medium, such that,in this latter case, it is not necessary to produce a lysate. In someembodiments, the reaction is started by injecting appropriate materials,e.g. coelenterazine, into a reaction chamber (e.g. a well of a multiwellplate such as a 96-well plate) containing the luciferase protein. Thereaction chamber may be situated in a reading device which can measurethe light output, e.g. using a luminometer or photomultiplier. The lightoutput or luminescence may also be measured over time, for example inthe same reaction chamber for a period of seconds, minutes, hours, etc.The light output or luminescence may be reported as the average overtime, the half-life of decay of signal, the sum of the signal over aperiod of time, or as the peak output.

Enhanced luminescence includes increased light output or luminescence,determined by suitable comparison of comparably-obtained measurements.As disclosed herein, one or more suitable amino acid substitutions tothe synthetic Oplophorus luciferase sequence produce modified luciferasepolypeptides which exhibit enhanced luminescence. Changes in thenucleotide sequence from the wild-type Oplophorus nucleotide sequencemay contribute to enhanced luminescence by leading to an amino acidsubstitution and/or by enhancing protein expression.

Enhanced signal stability includes an increase in how long the signalfrom a luciferase continues to luminesce, for example, as measured bythe half-life of decay of the signal in a time-course.

Enhanced protein stability includes increased thermal stability (e.g.stability at elevated temperatures) and chemical stability (e.g.stability in the presence of denaturants such as detergents, includinge.g. Triton X-100).

The term “OgLuc” refers to the mature 19 kDa subunit of the Oplophorusluciferase protein complex, i.e. without a signal sequence; the nativeform of the mature OgLuc polypeptide sequence is given in SEQ ID NO:1.The term “OgLuc variant” refers to a synthetic OgLuc with one or moreamino acid substitutions. For example, “OgLuc N166R variant” and“OgLuc+N166R” refers to a synthetic OgLuc which has an amino acidsubstitution of N to Rat position 166 relative to SEQ ID NO:1. The terms“WT,” “WT OgLuc,” and “wild-type OgLuc” refer to synthetic, mature OgLucprotein encoded by a synthetic polynucleotide with ACC at position 2relative to SEQ ID NO:1. The term “T2T” refers to a synthetic, matureOgLuc protein encoded by a synthetic polynucleotide with ACA at position2 relative to SEQ ID NO:1. For the data presented below in the Examples,the wild-type protein that was synthesized is the synthetic wild-typeprotein of SEQ ID NO:13, which is encoded by the nucleotide sequence ofSEQ ID NO:2.

The amino acid numbering used throughout this application to identifysubstituted residues is specified relative to the positions in themature wild-type OgLuc polypeptide sequence of SEQ ID NO:1. Thenaturally-occurring wild-type OgLuc sequence may be initiallysynthesized with other amino acids which are later cleaved, resulting inthe generation of a mature wild-type polypeptide such as shown in SEQ IDNO:1. For example, a signal sequence (e.g. to direct the nascent proteinto a particular organelle such as the endoplasmic reticulum and/or todirect the protein for secretion) may be present at the beginning of thenascent protein and may then be cleaved to produce the mature wild-typeprotein.

The substrate specificity of Oplophorus luciferase is unexpectedly broad(Inouye and Shimomura. BBRC 223:349(1997). For instance,bisdeoxycoelenterazine, an analogue of coelenterazine, is an excellentsubstrate for Oplophorus luciferase comparable to coelenterazine(Nakamura et al., Tetrahed. Lett., 38:6405 (1997)). Moreover, Oplophorusluciferase is a secreted enzyme, like the luciferase of the marineostracod Cypridina (Vargula) hilgendorfii (Johnson and Shimomura, Meth.Enzyme, 57:331 (1978)), which also uses an imidazopyrazinone-typeluciferin to emit light.

The molecular weight of Oplophorus luciferase was reported to be 130 kDa(by gel filtration) for the native protein complex, and 31 kDa aftertreatment with SDS (Shimomura et al., Biochem., 17:1994 (1978)). Theluciferase also showed a molecular weight of approximately 106 kDa ingel filtration, and it was found that the molecule separates into 35 kDaand 19 kDa proteins upon sodium dodecyl sulfate-polyacrylamide gelelectrophoresis (SDS-PAGE) analysis (Inouye et al., FEBS Lett., 481:19(2000)). Inouye et al. (2000) reported the molecular cloning of thecDNAs encoding the 35 kDa and 19 kDa proteins, and the identification ofthe protein component that catalyzes the luminescence reaction. ThecDNAs encoding the proteins were expressed in bacterial and mammaliancells as a 19 kDa protein which was capable of catalyzing theluminescent oxidation of coelenterazine (Inouye et al., 2000). Theprimary sequence of the 35 kDa protein revealed a leucine-rich repeatsequence, whereas the catalytic 19 kDa protein shared no homology withany known luciferases including various imidazopyrazinone luciferases(Inouye et al., 2000).

The 19 kDa protein (OgLuc) of Oplophorus luciferase appears to thesmallest catalytic component having luciferase function and its primarystructure has no significant homology with any reported luciferaseincluding imidazopyrazinone luciferases (Lorenz et al., PNAS USA,88:4438 (1991); Thompson et al., PNAS USA, 86:6567 (1989)). Inouye etal. (2000) reported that the overall amino acid sequence of the 19 kDaprotein appears similar to that of an E. coli amine oxidase (757 aminoacid residues; pir 140924) in the region of residues 217-392 (domain ofD3-S1) (Parson et al. Structure 3:1171 (1995)), whereas theamino-terminal region (3-49) of the same protein is homologous to theamino-terminal region (1-47) of a fatty acid binding protein (132 aminoacid residues; GenBank, L23322) (Becker et al., Gene, 148:321 (1994)).

Homology modeling requires the identification of at least one suitable3D structure template, usually an experimentally determined 3D structureof a homologous protein with significant sequence similarity to thetarget protein. OgLuc does not have significant sequence similarity toother known proteins. Therefore, fold recognition methods designed toidentify distant homologs of OgLuc, such as proteins with low sequencesimilarity to OgLuc, were employed. This approach yielded severalpotential 3D structure templates that belong to the protein family offatty acid binding proteins (FABPs), which is part of the calycinprotein superfamily. The model showed that the calycin fold structuralsignature, which effectively ties the N- and C-terminus together withhydrogen bonds, and which is present in at least three FABPs, is notcompletely conserved in OgLuc. OgLuc residue Asn166 (near theC-terminus) is unable to hydrogen bond with main chain carbonyls nearthe N-terminus. However, models of mutants containing either Arg or Lysat position 166 of OgLuc suggested that restoration of this structuremotif could improve the structural stability of OgLuc and itsexpression/activity in cells.

Embodiments of the invention provide a synthetic, modified (variant)luciferase, as well as fragments thereof, for instance, those useful incomplementation assays, having at least one amino acid substitutionrelative to a corresponding wild-type luciferase in a region that isstructurally homologous to a member of the calycin protein superfamily,e.g., the family of fatty acid binding proteins. In one embodiment, theinvention provides a modified crustacean luciferase, e.g., a modifieddecapod luciferase, as well as fragments thereof, for instance, thoseuseful in complementation assays, having at least one amino acidsubstitution relative to a corresponding wild-type crustaceanluciferase, in a region that is structurally homologous to a member ofthe calycin protein superfamily, e.g., the family of fatty acid bindingproteins. In one embodiment, the invention provides a modifiedluciferase of a eukaryotic unicellular flagellate, as well as fragmentsthereof, for instance, those useful in complementation assays, having atleast one amino acid substitution relative to a corresponding wild-typeeukaryotic unicellular flagellate luciferase, e.g., luciferases fromDinoflagellata including Dinophyceae, Noctiluciphyceae, orSyndiniophycea, in a region that is structurally homologous to a memberof the calycin protein superfamily, e.g., the family of fatty acidbinding proteins. A nucleic acid molecule encoding the modifiedluciferase may or may not encode a secretory signal peptide linked tothe modified luciferase.

The at least one substitution in the synthetic modified luciferase, or afragment thereof, is to an amino acid residue at a correspondingposition in the region that is structurally homologous to a member ofthe calycin protein superfamily, e.g., the family of fatty acid bindingproteins, which residue may participate in intramolecular hydrogen orionic bond formation, and is associated with enhanced luminescence, inthe modified luciferase. Enhanced luminescence includes but is notlimited to increased light emission, altered kinetics of light emission,e.g., greater stability of the light intensity, or altered luminescencecolor, e.g., a shift towards shorter or longer wavelengths, or acombination thereof. In one embodiment, the residue in the syntheticmodified luciferase at the corresponding position may interact with aresidue in a region corresponding to residues 1 to 10 or 144 to 148 ofOgLuc , e.g., one having SEQ ID NO:1 (note that the numbering of thosepositions is based on a Phe at residue 1 of the mature sequence not aMet; however, other residues may precede the Phe such as a Val atposition −1 which may be introduced by insertion of a cloning site) or aresidue with atoms that are within 4 to 8 Å, e.g., within 6 Å, of theresidue at the corresponding position (position 166). Correspondingpositions may be identified by aligning sequences using, for instance,sequence alignment programs, secondary structure prediction programs orfold recognition methods, or a combination thereof. The modifiedluciferase in accordance with the invention may include additional aminoacid substitutions that alter the color of luminescence, for example,substitution(s) that result in red-shifted luminescence, alter signalstability, alter protein stability, or any combination thereof.

In one embodiment, the invention provides a modified decapod luciferasewhich has enhanced luminescence relative to a corresponding wild-typedecapod luciferase. In another embodiment, the invention provides amodified decapod luciferase which utilizes coelenterazine.Coelenterazines include but are not limited to naturally occurringcoelenterazines as well as derivatives (analogs) thereof, such as thosedisclosed in U.S. Pat. No. 7,118,878, as well as EnduRen, ViviRen,coelenterazine n, coelenterazine h, coelenterazine c, coelenterazine cp,coelenterazine e, coelenterazine f, coelenterazine fcp, coelenterazinehh, coelenterazine i, coelenterazine icp, 2-methyl coelenterazine, andthose disclosed in WO/040100 and U.S. application Ser. No. 12/056,073,the disclosures of which are incorporated by reference herein.

The modified luciferase in accordance with the invention has a residueother than asparagine at a position corresponding to residue 166 in SEQID NO:1 that results in the enhanced luminescence and optionally anaspartic acid at a position corresponding to residue 5 in SEQ ID NO:1, aglycine at a position corresponding to residue 8 in SEQ ID NO:1, anaspartic acid at a position corresponding to residue 9 in SEQ ID NO:1, atryptophan, tyrosine or phenylalanine at a position corresponding toresidue 10 in SEQ ID NO:1, an asparagine at a position corresponding toresidue 144 in SEQ ID NO:1, and/or a glycine at a position correspondingto residue 147 in SEQ ID NO:1, or any combination thereof. In oneembodiment, the residue in the modified luciferase corresponding toresidue 166 in SEQ ID NO:1 is lysine. In another embodiment, the residuein the modified luciferase corresponding to residue 166 in SEQ ID NO:1is arginine. In one embodiment, the residue in the modified luciferasecorresponding to residue 166 in SEQ ID NO:1 is capable of forming one ormore intramolecular hydrogen or ionic bonds with carbonyls or the sidechain at a position corresponding to residue 9 in SEQ ID NO:1 near theN-terminus of the modified luciferase. In one embodiment, the modifiedluciferase lacks a signal peptide sequence. In one embodiment, themodified luciferase has at least 60%, e.g., at least 65%, 70%, 75%, 80%,85%, 90%, 95%, 96%, 97%, 98%,or 99%, but less than 100%, amino acidsequence identity to SEQ ID NO:1.

In one embodiment, the corresponding wild-type luciferase is anOplophorus luciferase, e.g., Oplophorus gracilirostris, Oplophorusgrimaldii, Oplophorus spinicauda, Oplophorus foliaceus, Oplophorusnoraezeelandiae, Oplophorus typus, Oplophorus noraezelandiae orOplophorus spinous, Heterocarpus luciferase, Systellapis luciferase oran Acanthephyra luciferase. In one embodiment, the modified luciferasehas at least a 2-fold or more, e.g., at least 4-fold, increasedluminescence emission in a prokaryotic cell and/or an eukaryotic cellrelative to the corresponding wild-type luciferase.

In another embodiment, the invention provides a modified dinoflagellateluciferase which has enhanced luminescence relative to a correspondingwild-type dinoflagellate luciferase, e.g., a dinoflagellate luciferasesuch as a Lingulodinium polyedrum luciferase, a Pyrocystis lunulaluciferase or one having SEQ ID NO:21. The modified luciferase may havea residue other than asparagine at a position corresponding to residue166 in SEQ ID NO:1, e.g., an arginine, and optionally a proline at aposition corresponding to residue 5 in SEQ ID NO:1, a glycine at aposition corresponding to residue 8 in SEQ ID NO:1, an arginine at aposition corresponding to residue 9 in SEQ ID NO:1, a tryptophan,tyrosine or phenylalanine at a position corresponding to residue 10 inSEQ ID NO:1, a phenylalanine at a position corresponding to residue 144in SEQ ID NO:1, and/or a threonine at a position corresponding toresidue 147 in SEQ ID NO:1, or any combination thereof. In oneembodiment, the residue in the modified luciferase corresponding toresidue 166 in SEQ ID NO:1 is lysine. In another embodiment, the residuein modified luciferase corresponding to residue 166 in SEQ ID NO:1 isarginine. In one embodiment, the residue in the modified luciferasecorresponding to residue 166 in SEQ ID NO:1 is capable of forming one ormore intramolecular hydrogen or ionic bonds with carbonyls or the sidechain at a position corresponding to residue 9 in SEQ ID NO:1 near theN-terminus of modified luciferase. In one embodiment, the modifiedluciferase lacks a signal peptide sequence.

In one embodiment, the modified luciferase has at least 60%, e.g., atleast 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%,or 99%, but lessthan 100%, amino acid sequence identity to SEQ ID NO:21. The modifiedluciferase of the invention, including one with additional amino acidsubstitutions that alter the color of luminescence, may be employed witha modified luciferin in a luminogenic reaction that produces an alteredluminescence color.

Further provided is a modified luciferase having a FABP beta-barrelrelated 3D structural domain, which modified luciferase has asubstitution that results in the noncovalent joining, e.g., viaintramolecular hydrogen or ionic bonds, of the terminal beta sheets ofthe beta barrel, and optionally additional noncovalent bonds, e.g., viaintramolecular hydrogen or ionic bonds, with adjacent secondarystructures.

Embodiments of the invention also provide a modified decapod ordinoflagellate luciferase which has enhanced luminescence and anarginine, lysine, alanine, leucine, proline, glutamine or serine at aposition corresponding to residue 166 in SEQ ID NO:1 and at least oneamino acid substitution relative to a corresponding wild-type decapod ordinoflagellate luciferase. In one embodiment, the at least one aminoacid substitution in the modified luciferase is a substitution at aposition corresponding to residue 4, 11, 33, 44, 45, 54, 75, 104, 115,124, 135, 138, 139, 167, or 169, ora combination thereof, in SEQ IDNO:1, e.g., one which results in enhanced luminescence relative to amodified luciferase which has enhanced luminescence and an arginine,lysine, alanine, leucine, proline, glutamine or serine at a positioncorresponding to residue 166 in SEQ ID NO:1.

In one embodiment, the modified luciferase of the invention has one ormore heterologous amino acid sequences at the N-terminus, C-terminus, orboth (a fusion polypeptide such as one with an epitope or fusion tag),which optionally directly or indirectly interact with a molecule ofinterest. In one embodiment, the presence of the heterologoussequence(s) does not substantially alter the luminescence of themodified luciferase either before or after the interaction with themolecule of interest. In one embodiment, the heterologous amino acidsequence is an epitope tag. In another embodiment, the heterologousamino acid sequence is one which, during or after interaction with amolecule of interest, undergoes a conformational change, which in turnalters the activity of the luciferase, e.g., a modified OgLuc with suchan amino acid sequence is useful to detect allosteric interactions. Themodified luciferase or a fusion with the modified luciferase or afragment thereof may be employed as a reporter.

In one embodiment, a fragment of a luciferase of the invention is fusedto a heterologous amino acid sequence, the fusion thereby forming abeta-barrel, which fusion protein is capable of generating luminescencefrom a naturally occurring luciferin or a derivative thereof.

Also provided is a polynucleotide encoding a modified luciferase of theinvention or a fusion thereof, an isolated host cell having thepolynucleotide or the modified luciferase or a fusion thereof, andmethods of using the polynucleotide, modified luciferase or a fusionthereof or host cell of the invention.

Further provided is a method to identify amino acid positions in aprotein of interest which are in different secondary structures, e.g.,structures separated by 5 amino acids or more that are not part ofeither secondary structure, and are capable of hydrogen or ionic bondformation with each other. The method includes comparing secondarystructures predicted for the amino acid sequence of a protein ofinterest to secondary structures of one or more proteins without overallsequence similarly, e.g., less than 30% identity to the protein ofinterest. The one or more proteins have a defined 3D structure and atleast one of the proteins has a first residue associated with at leastone first secondary structure which forms a hydrogen or ionic bond,e.g., salt bridges, between side chains or between a side chain of or amain chain carbonyl near or within 5 or 10 residues of a second residueassociated with a second secondary structure, respectively. In oneembodiment, the first secondary structure is C-terminal to the secondsecondary structure. In another embodiment, the first secondarystructure is N-terminal to the second secondary structure. Then it isdetermined whether the protein of interest has one or more secondarystructures corresponding to at least the first secondary structure inthe one or more proteins and if so determining amino acid positions inthe protein of interest that correspond to the first residue, the secondresidue, or both, in the one or more proteins. In one embodiment, onesecondary structure is a 3₁₀ helix or a beta-barrel. In one embodiment,the protein of interest is a luciferase. In one embodiment, the firstresidue is capable of forming a hydrogen or ionic bond to one or moremain chain carbonyls within 5 residues of the second residue. In oneembodiment, the one or more proteins are fatty acid binding proteins.

Definitions

Amino acid residues in the modified luciferases of the invention may bethose in the L-configuration, the D-configuration or nonnaturallyoccurring amino acids such as norleucine, L-ethionine,β-2-thienylalanine, 5-methyltryptophan norvaline, L-canavanine,p-fluorophenylalAnine, p-(4-hydroxybenzoyl)phenylalanine,2-keto-4-(methylthio)butyric acid, beta-hydroxy leucine,gamma-chloronorvaline, gamma-methyl D-leucine, beta-D-L hydroxyleucine,2-amino-3-chlorobutyric acid, N-methyl-D-valine,3,4,difluoro-L-phenylalanine, 5,5,5-trifluoroleucine,4,4,4,-trifluoro-L-valine, 5-fluoro-L-tryptophan,4-azido-L-phenylalanine, 4-benzyl-L-phenylalanine, thiaproline,5,5,5-trifluoroleucine, 5,5,5,5′,5′,5′-hexafluoroleucine,2-amino-4-methyl-4-pentenoic acid,2-amino-3,3,3-trifluoro-methylpentanoic acid,2-amino-3-methyl-5,5,5-tri-fluoropentanoic acid,2-amino-3-methyl-4-pentenoic acid, trifluorovaline, hexafluorovaline,homocysteine, hydroxylysine, ornithine, and those with peptide linkagesoptionally replaced by a linkage such as, —CH₂NH—, —CH₂S—, —CH₂-CH₂—,—CH═CH— (cis and trans), —COCH₂—, —CH(OH)CH₂—, and —CH₂SO—, by methodsknown in the art. In keeping with standard polypeptide nomenclature,abbreviations for naturally occurring amino acid residues are as shownin the following Table of Correspondence.

TABLE OF CORRESPONDENCE 1-Letter 3-Letter AMINO ACID Y Tyr L-tyrosine GGly L-glycine F Phe L-phenylalanine M Met L-methionine A Ala L-alanine SSer L-serine I Ile L-isoleucine L Leu L-leucine T Thr L-threonine V ValL-valine P Pro L-proline K Lys L-lysine H His L-histidine Q GlnL-glutamine E Glu L-glutamic acid W Trp L-tryptophan R Arg L-arginine DAsp L-aspartic acid N Asn L-asparagine C Cys L-cysteine

Enhanced luminescence, as used herein, may include any of the following:increased light emission, altered kinetics of light emission, e.g.,greater stability of the light intensity, or altered luminescence color,e.g., a shift towards shorter or longer wavelengths.

The term “homology” refers to a degree of complementarity between two ormore sequences. There may be partial homology or complete homology(i.e., identity). Homology is often measured using sequence analysissoftware (e.g., “GCG” and “Seqweb” Sequence Analysis Software Packageformerly sold by the Genetics Computer Group. University of WisconsinBiotechnology Center. 1710 University Avenue. Madison, Wis. 53705). Suchsoftware matches similar sequences by assigning degrees of homology tovarious substitutions, deletions, insertions, and other modifications.Conservative substitutions typically include substitutions within thefollowing groups: glycine, alanine; valine, isoleucine, leucine;aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine;lysine, arginine; and phenylalanine, tyrosine.

The term “isolated” when used in relation to a nucleic acid or apolypeptide, as in “isolated oligonucleotide”, “isolatedpolynucleotide”, “isolated protein”, or “isolated polypeptide” refers toa nucleic acid or amino acid sequence that is identified and separatedfrom at least one contaminant with which it is ordinarily associated inits source. Thus, an isolated nucleic acid or isolated polypeptide ispresent in a form or setting that is different from that in which it isfound in nature. In contrast, non-isolated nucleic acids (e.g., DNA andRNA) or non-isolated polypeptides (e.g., proteins and enzymes) are foundin the state they exist in nature. For example, a given DNA sequence(e.g., a gene) is found on the host cell chromosome in proximity toneighboring genes; RNA sequences (e.g., a specific mRNA sequenceencoding a specific protein), are found in the cell as a mixture withnumerous other mRNAs that encode a multitude of proteins. However,isolated nucleic acid includes, by way of example, such nucleic acid incells ordinarily expressing that nucleic acid where the nucleic acid isin a chromosomal location different from that of natural cells, or isotherwise flanked by a different nucleic acid sequence than that foundin nature. The isolated nucleic acid or oligonucleotide may be presentin single-stranded or double-stranded form. When an isolated nucleicacid or oligonucleotide is to be utilized to express a protein, theoligonucleotide contains at a minimum, the sense or coding strand (i.e.,a single-stranded nucleic acid), but may contain both the sense andanti-sense strands (i.e., a double-stranded nucleic acid).

The term “nucleic acid molecule,” “polynucleotide” or “nucleic acidsequence” as used herein, refers to nucleic acid, DNA or RNA thatcomprises coding sequences necessary for the production of a polypeptideor protein precursor. The encoded polypeptide may be a full-lengthpolypeptide, a fragment thereof (less than full-length), or a fusion ofeither the full-length polypeptide or fragment thereof with anotherpolypeptide, yielding a fusion polypeptide.

“Oplophorus luciferase” is a complex of native 35 kDa and 19 kDaproteins. The 19 kDa protein is the smallest catalytic component(GenBank accession BAB13776, 196 amino acids). As used herein, OgLuc isthe 19 kDa protein without signal peptide (169 amino acids, residues 28to 196 of BAB13776).

By “peptide,” “protein” and “polypeptide” is meant any chain of aminoacids, regardless of length or post-translational modification (e.g.,glycosylation or phosphorylation). The nucleic acid molecules of theinvention encode a variant of a naturally-occurring protein orpolypeptide fragment thereof, which has an amino acid sequence that isat least 60%, e.g., at least 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%,97%, 98%, or 99%, but less than 100%, amino acid sequence identity tothe amino acid sequence of the naturally-occurring (native or wild-type)protein from which it is derived. The term “fusion polypeptide” or“fusion protein” refers to a chimeric protein containing a referenceprotein (e.g., luciferase) joined at the N- and/or C-terminus to one ormore heterologous sequences (e.g., a non-luciferase polypeptide).

Protein primary structure (primary sequence, peptide sequence, proteinsequence) is the sequence of amino acids. It is generally reportedstarting from the amino-terminal (N) end to the carboxyl-terminal (C)end. Protein secondary structure can be described as the localconformation of the peptide chain, independent of the rest of theprotein. There are ‘regular’ secondary structure elements (e.g.,helices, sheets or strands) that are generally stabilized by hydrogenbond interactions between the backbone atoms of the participatingresidues, and ‘irregular’ secondary structure elements (e.g., turns,bends, loops, coils, disordered or unstructured segments). Proteinsecondary structure can be predicted with different methods/programs,e.g., PSIPRED (McGuffin et al., Bioinformatics, 16:404 (2000)), PORTER(Pollastri et al., Bioinformatics, 21:1719 (2005)), DSC (King andSternberg, Protein Sci., 5:2298 (1996)), seehttp://www.expasy.org/tools/#secondary for a list. Protein tertiarystructure is the global three-dimensional (3D) structure of the peptidechain. It is described by atomic positions in three-dimensional space,and it may involve interactions between groups that are distant inprimary structure. Protein tertiary structures are classified intofolds, which are specific three-dimensional arrangements of secondarystructure elements. Sometimes there is no discernable sequencesimilarity between proteins that have the same fold.

The term “wild-type” or “native” as used herein, refers to a gene orgene product that has the characteristics of that gene or gene productisolated from a naturally occurring source. A wild-type gene is thatwhich is most frequently observed in a population and is thusarbitrarily designated the “wild-type” form of the gene. In contrast,the term “mutant” refers to a gene or gene product that displaysmodifications in sequence and/or functional properties (i.e., alteredcharacteristics) when compared to the wild-type gene or gene product. Itis noted that naturally occurring mutants can be isolated; these areidentified by the fact that they have altered characteristics whencompared to the wild-type gene or gene product.

I. Exemplary Polynucleotides and Proteins

The invention includes a modified luciferase or protein fragmentsthereof, e.g., those with deletions, for instance a deletion of 1 toabout 5 residues, and chimeras (fusions) thereof (see U.S. applicationSer. Nos. 60/985,585 and 11/732,105, the disclosures of which areincorporated by reference herein) having at least one amino acidsubstitution relative to a wild-type luciferase, which substitutionresults in the modified luciferase having enhanced stability, enhancedluminescence, e.g., increased luminescence emission, greater stabilityof the luminescence kinetics, or altered luminescence color, or both.The luciferase sequences of a modified luciferase are substantially thesame as the amino acid sequence of a corresponding wild-type luciferase.A polypeptide or peptide having substantially the same sequence meansthat an amino acid sequence is largely, but is not entirely, the sameand retains the functional activity of the sequence to which it isrelated. In general, two amino acid sequences are substantially the sameor substantially homologous if they are at least 60%, e.g., at least65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99%, but less than100%, amino acid sequence identity. In one embodiment, the modifiedluciferase is encoded by a recombinant polynucleotide.

Homology or identity may be often measured using sequence analysissoftware. Such software matches similar sequences by assigning degreesof homology to various deletions, substitutions and other modifications.The terms “homology” and “identity” in the context of two or morenucleic acids or polypeptide sequences, refer to two or more sequencesor subsequences that are the same or have a specified percentage ofamino acid residues or nucleotides that are the same when compared andaligned for maximum correspondence over a comparison window ordesignated region as measured using any number of sequence comparisonalgorithms or by manual alignment and visual inspection.

For sequence comparison, typically one sequence acts as a referencesequence, to which test sequences are compared. When using a sequencecomparison algorithm, test and reference sequences are entered into acomputer, subsequence coordinates are designated, if necessary, andsequence algorithm program parameters are designated. Default programparameters can be used, or alternative parameters can be designated. Thesequence comparison algorithm then calculates the percent sequenceidentities for the test sequences relative to the reference sequence,based on the program parameters.

Methods of alignment of sequence for comparison are well-known in theart. Optimal alignment of sequences for comparison can be conducted bythe local homology algorithm of Smith et al. (1981), by the homologyalignment algorithm of Needleman et al. (J. Mol. Biol., 48:443 (1970),by the search for similarity method of Person et al. (Proc. Natl. Acad.Sci. USA, 85, 2444 (1988)), by computerized implementations of thesealgorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin GeneticsSoftware Package, Genetics Computer Group, 575 Science Dr., Madison,Wis.), or by manual alignment and visual inspection.

Computer implementations of these mathematical algorithms can beutilized for comparison of sequences to determine sequence identity.Such implementations include, but are not limited to: CLUSTAL in thePC/Gene program (available from Intelligenetics, Mountain View, Calif.);the ALIGN program (Version 2.0) and GAP, BESTFIT, BLAST, FASTA, andTFASTA in the Wisconsin Genetics Software Package, Version 8 (availablefrom Genetics Computer Group (GCG), 575 Science Drive, Madison, Wis.,USA). Alignments using these programs can be performed using the defaultparameters. The CLUSTAL program is well described by Higgins et al.,Gene, 73:237 (1988); Higgins et al., CABIOS, 5:157 (1989); Corpet etal., Nucl. Acids Res., 16:1088 (1988); Huang et al., CABIOS, 8:155(1992); and Pearson et al., Methods Mol. Biol., 24:307 (1994). The ALIGNprogram is based on the algorithm of Myers and Miller, LABIOS, 4:11(1988). The BLAST programs of Altschul et al. (J. Mol. Biol., 215:403(1990)) are based on the algorithm of Karlin and Altschul (PNAS USA,90:5873 (1993)).

Software for performing BLAST analyses is publicly available through theNational Center for Biotechnology Information(http://www.ncbi.nlm.nih.gov/). This algorithm involves firstidentifying high scoring sequence pairs (HSPs) by identifying shortwords of length W in the query sequence, which either match or satisfysome positive-valued threshold score T when aligned with a word of thesame length in a database sequence. T is referred to as the neighborhoodword score threshold (Altschul et al., J. Mol. Biol., 215:403 (1990)).These initial neighborhood word hits act as seeds for initiatingsearches to find longer HSPs containing them. The word hits are thenextended in both directions along each sequence for as far as thecumulative alignment score can be increased. Cumulative scores arecalculated using, for nucleotide sequences, the parameters M (rewardscore for a pair of matching residues; always >0) and N (penalty scorefor mismatching residues; always <0). For amino acid sequences, ascoring matrix is used to calculate the cumulative score. Extension ofthe word hits in each direction are halted when the cumulative alignmentscore falls off by the quantity X from its maximum achieved value, thecumulative score goes to zero or below due to the accumulation of one ormore negative-scoring residue alignments, or the end of either sequenceis reached.

In addition to calculating percent sequence identity, the BLASTalgorithm also performs a statistical analysis of the similarity betweentwo sequences (see, e.g., Karlin and Altschul, PNAS USA, 90:5873 (1993).One measure of similarity provided by the BLAST algorithm is thesmallest sum probability (P(N)), which provides an indication of theprobability by which a match between two nucleotide or amino acidsequences would occur by chance. For example, a test nucleic acidsequence is considered similar to a reference sequence if the smallestsum probability in a comparison of the test nucleic acid sequence to thereference nucleic acid sequence is less than about 0.1, more preferablyless than about 0.01, and most preferably less than about 0.001.

To obtain gapped alignments for comparison purposes, Gapped BLAST (inBLAST 2.0) can be utilized as described in Altschul et al. (Nuc. AcidsRes., 25:3389 (1997)). Alternatively, PSI-BLAST (in BLAST 2.0) can beused to perform an iterated search that detects distant relationshipsbetween molecules. See Altschul et al., supra. When utilizing BLAST,Gapped BLAST, PSI-BLAST, the default parameters of the respectiveprograms (e.g., BLASTN for nucleotide sequences, BLASTX for proteins)can be used. The BLASTN program (for nucleotide sequences) uses asdefaults a wordlength (W) of 11, an expectation (E) of 10, a cutoff of100, M=5, N=−4, and a comparison of both strands. For amino acidsequences, the BLASTP program uses as defaults a wordlength (W) of 3, anexpectation (E) of 10, and the BLOSUM62 scoring matrix (see Henikoff andHenikoff, PNAS USA, 89:10915 (1989)). See “www.ncbi.nlm.nih.gov.”

In particular, a polypeptide may be substantially related to another(reference) polypeptide but for a conservative or nonconservativevariation. A conservative variation denotes the replacement of an aminoacid residue by another, biologically similar residue includingnaturally occurring or nonnaturally occurring amino acid residues.Examples of conservative variations include the substitution of onehydrophobic residue such as isoleucine, valine, leucine or methioninefor another, or the substitution of one polar residue for another suchas the substitution of arginine for lysine, glutamic for aspartic acids,or glutamine for asparagine, and the like. Other illustrative examplesof conservative substitutions include the changes of: alanine to serine;arginine to lysine; asparagine to glutamine or histidine; aspartate toglutamate; cysteine to serine; glutamine to asparagine; glutamate toaspartate; glycine to proline; histidine to asparagine or glutamine;isoleucine to leucine or valine; leucine to valine or isoleucine; lysineto arginine, glutamine, or glutamate; methionine to leucine orisoleucine; phenylalanine to tyrosine, leucine or methionine; serine tothreonine; threonine to serine; tryptophan to tyrosine; tyrosine totryptophan or phenylalanine; valine to isoleucine to leucine. A modifiedluciferase of the invention has a conservative or a nonconservativesubstitution which results in enhanced stability, luminescence, or both.

The modified luciferase proteins or fusion proteins of the invention maybe prepared by recombinant methods or by solid phase chemical peptidesynthesis methods. Such methods are known in the art.

II. Vectors and Host Cells Encoding the Modified Luciferase or FusionsThereof

Once a desirable nucleic acid molecule encoding a modified luciferase, afragment thereof, such as one with luminescence activity or which may becomplemented by another molecule to result in luminescence activity, ora fusion thereof with luminescence activity, is prepared, an expressioncassette encoding the modified luciferase, a fragment thereof, e.g., onefor complementation, or a fusion thereof with luminescence activity, maybe prepared. For example, a nucleic acid molecule comprising a nucleicacid sequence encoding a modified luciferase is optionally operablylinked to transcription regulatory sequences, e.g., one or moreenhancers, a promoter, a transcription termination sequence or acombination thereof, to form an expression cassette. The nucleic acidmolecule or expression cassette may be introduced to a vector, e.g., aplasmid or viral vector, which optionally includes a selectable markergene, and the vector introduced to a cell of interest, for example, aprokaryotic cell such as E. coli, Streptomyces spp., Bacillus spp.,Staphylococcus spp. and the like, as well as eukaryotic cells includinga plant (dicot or monocot), fungus, yeast, e.g., Pichia, Saccharomycesor Schizosaccharomyces, or a mammalian cell, lysates thereof, or to anin vitro transcription/translation mixture. Mammalian cells include butare not limited to bovine, caprine, ovine, canine, feline, non-humanprimate, e.g., simian, and human cells. Mammalian cell lines include,but are not limited to, CHO, COS, 293, HeLa, CV-1, SH-SY5Y, HEK293, andNIH3T3 cells.

The expression of an encoded modified luciferase may be controlled byany promoter capable of expression in prokaryotic cells or eukaryoticcells including synthetic promoters. Prokaryotic promoters include, butare not limited to, SP6, T7, T5, tac, bla, trp, gal, lac or maltosepromoters, including any fragment that has promoter activity. Eukaryoticpromoters include, but are not limited to, constitutive promoters, e.g.,viral promoters such as CMV, SV40 and RSV promoters, as well asregulatable promoters, e.g., an inducible or repressible promoter suchas the tet promoter, the hsp70 promoter and a synthetic promoterregulated by CRE, including any fragment that has promoter activity. Thenucleic acid molecule, expression cassette and/or vector of theinvention may be introduced to a cell by any method including, but notlimited to, calcium-mediated transformation, electroporation,microinjection, lipofection and the like.

III. Optimized Sequences, and Vectors and Host Cells Encoding theModified Luciferase

Also provided is an isolated nucleic acid molecule (polynucleotide)comprising a nucleic acid sequence encoding a modified luciferase of theinvention, a fragment thereof or a fusion thereof. In one embodiment,the isolated nucleic acid molecule comprises a nucleic acid sequencewhich is optimized for expression in at least one selected host.Optimized sequences include sequences which are codon optimized, i.e.,codons which are employed more frequently in one organism relative toanother organism, e.g., a distantly related organism, as well asmodifications to add or modify Kozak sequences and/or introns, and/or toremove undesirable sequences, for instance, potential transcriptionfactor binding sites. Such optimized sequences can produced enhancedexpression, e.g. increased levels of protein expression, when introducedinto a host cell.

In one embodiment, the polynucleotide includes a nucleic acid sequenceencoding a modified luciferase of the invention, which nucleic acidsequence is optimized for expression in a mammalian host cell. In oneembodiment, an optimized polynucleotide no longer hybridizes to thecorresponding non-optimized sequence, e.g., does not hybridize to thenon-optimized sequence under medium or high stringency conditions. Theterm “stringency” is used in reference to the conditions of temperature,ionic strength, and the presence of other compounds, under which nucleicacid hybridizations are conducted. With “high stringency” conditions,nucleic acid base pairing will occur only between nucleic acid fragmentsthat have a high frequency of complementary base sequences. Thus,conditions of “medium” or “low” stringency are often required when it isdesired that nucleic acids that are not completely complementary to oneanother be hybridized or annealed together. The art knows well thatnumerous equivalent conditions can be employed to comprise medium or lowstringency conditions.

In another embodiment, the polynucleotide has less than 90%, e.g., lessthan 80%, nucleic acid sequence identity to the correspondingnon-optimized sequence and optionally encodes a polypeptide having atleast 60%, e.g., at least 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, or 99%, but less than 100%, amino acid sequence identity with thepolypeptide encoded by the non-optimized sequence. Constructs, e.g.,expression cassettes, and vectors comprising the isolated nucleic acidmolecule, e.g., with optimized nucleic acid sequence, as well as kitscomprising the isolated nucleic acid molecule, construct or vector arealso provided.

A nucleic acid molecule comprising a nucleic acid sequence encoding amodified luciferase of the invention, a fragment thereof or a fusionthereof is optionally optimized for expression in a particular host celland also optionally operably linked to transcription regulatorysequences, e.g., one or more enhancers, a promoter, a transcriptiontermination sequence or a combination thereof, to form an expressioncassette.

In one embodiment, a nucleic acid sequence encoding a modifiedluciferase of the invention, a fragment thereof or a fusion thereof isoptimized by replacing codons, e.g., at least 25% of the codons, in awild type luciferase sequence with codons which are preferentiallyemployed in a particular (selected) cell. Preferred codons have arelatively high codon usage frequency in a selected cell, and preferablytheir introduction results in the introduction of relatively fewtranscription factor binding sites for transcription factors present inthe selected host cell, and relatively few other undesirable structuralattributes. Thus, the optimized nucleic acid product may have animproved level of expression due to improved codon usage frequency, anda reduced risk of inappropriate transcriptional behavior due to areduced number of undesirable transcription regulatory sequences.

An isolated and optimized nucleic acid molecule may have a codoncomposition that differs from that of the corresponding wild typenucleic acid sequence at more than 30%, 35%, 40% or more than 45%, e.g.,50%, 55%, 60% or more of the codons. Exemplary codons for use in theinvention are those which are employed more frequently than at least oneother codon for the same amino acid in a particular organism and, in oneembodiment, are also not low-usage codons in that organism and are notlow-usage codons in the organism used to clone or screen for theexpression of the nucleic acid molecule. Moreover, codons for certainamino acids (i.e., those amino acids that have three or more codons),may include two or more codons that are employed more frequently thanthe other (non-preferred) codon(s). The presence of codons in thenucleic acid molecule that are employed more frequently in one organismthan in another organism results in a nucleic acid molecule which, whenintroduced into the cells of the organism that employs those codons morefrequently, is expressed in those cells at a level that is greater thanthe expression of the wild type or parent nucleic acid sequence in thosecells.

In one embodiment of the invention, the codons that are different arethose employed more frequently in a mammal, while in another embodimentthe codons that are different are those employed more frequently in aplant. Preferred codons for different organisms are known to the art,e.g., see www.kazusa.or.jp./codon/. A particular type of mammal, e.g., ahuman, may have a different set of preferred codons than another type ofmammal. Likewise, a particular type of plant may have a different set ofpreferred codons than another type of plant. In one embodiment of theinvention, the majority of the codons that differ are ones that arepreferred codons in a desired host cell. Preferred codons for organismsincluding mammals (e.g., humans) and plants are known to the art (e.g.,Wada et al., Nucl. Acids Res., 18:2367 (1990); Murray et al., Nucl.Acids Res., 17:477 (1989)).

IV. Exemplary Luciferase for Stability Enhancement

The luciferase secreted from the deep-sea shrimp Oplophorusgracilirostris has been shown to possess many interestingcharacteristics, such as high activity, high quantum yield, and broadsubstrate specificity (coelenterazine, coelenterazine analogs). Thebioluminescent reaction of Oplophorus takes place when the oxidation ofcoelenterazine (the luciferin) with molecular oxygen is catalyzed byOplophorus luciferase, resulting in light of maximum intensity at 462 nmand the products CO₂ and coelenteramide (Shimomura et al., Biochemistry,17:994 (1978); this differs from Inouye 2000 which mentions 454 nm).Optimum luminescence occurs at pH 9 in the presence of 0.05-0.1 M NaClat 40° C., and, due to the unusual resistance of this enzyme to heat,visible luminescence occurs at temperatures above 50° C. when the highlypurified enzyme is used, or at over 70° C. when partially purifiedenzyme is used. At pH 8.7, the native luciferase has a molecular weightof approximately 130,000, apparently comprising 4 monomers of 31,000; atlower pHs, the native luciferase tends to polymerize.

The mature protein consists of 19 kDa and 35 kDa proteins(heterotetramer consisting of two 19 kDa components and two 35 kDacomponents). The 19 kDa protein (OgLuc) has been overexpressed as amonomer in E. coli and shown to be active, however, it is producedpredominantly as inclusion bodies. The formation of inclusion bodies islikely due to the instability of the protein inside of the cell.

A 3D structure of OgLuc is not available. In addition, there are noknown homology-based models available, as OgLuc does not have anysequence homology to other luciferases and no significant overallsequence similarity to other known proteins. In order to generate amodel, a fold recognition method designed to identify distant homologousproteins was used. Using this approach, as described hereinbelow, a setof fatty acid binding proteins (FABPs) belonging to the calycin proteinsuperfamily was identified, and an OgLuc homology model was generatedbased on the 3D structures of three of these FABPs.

Calycins are a protein superfamily whose members share similar β-barrelstructures. Members include, but are not limited to, fatty acid bindingproteins (FABPs) and lipocalins. The FABP protein family has aten-stranded discontinuous β-barrel structure; the avidin and MPIbarrels, although eight-stranded, are more circular in cross-sectionthan that of the lipocalins and do not have a C-terminal helix or strandI; while triabin has a similar barrel geometry yet has a modifiedtopology. The N- and C-terminal strands of the FABPs and lipocalins canbe closely superimposed, with the loss (FABP to lipocalin) or gain(lipocalin to FABP) of two central strands necessary to effect thetransformation of one to another (Flower et al., Protein Science, 2:753(1993)). Moreover, beyond some functional similarity (hydrophobic ligandbinding and/or macromolecular interaction) these families arecharacterized by a similar folding pattern (an antiparallel β-barreldominated by a largely +I topology), within which large parts of theirstructures can be structurally equivalenced, although the families shareno global sequence similarity.

Previous work (Flower, Protein Pept. Lett., 2:341 (1995)) has shown thatmembers of the calycin superfamily also share a distinct structuralpattern. An arginine or lysine residue (from the last strand of theβ-barrel) which forms hydrogen bonds to the main-chain carbonyl groupsof the N-terminal 3₁₀-like helix and packs across a conserved tryptophan(from the first strand of the β-barrel). This pattern can be seen bothin the structures of kernel lipocalins, which also share a conservedinteraction from loop L6, and in the more structurally diverse outlierlipocalins. It is also apparent in the other four families comprisingthe calycins. Examination of the available structures of streptavidinand chicken avidin, the metalloproteinase inhibitor from Erwiniachrysanthemi, and the structure of triabin, all reveal a very similararrangement of interacting residues. Most of the known FABPs have anarrangement of side chain interactions similar to those described above,in which a tryptophan, from the first strand of the FABP barrel, packsagainst an arginine from near the end of the last. This feature is,however, lacking from a group of more highly diverged FABPs, typified byinsect muscle FABPs.

The OgLuc homology model shows that the calycin fold structuralsignature, which effectively ties the N- and C-terminus together withhydrogen bonds, and which is present in the three FABPs, is notcompletely conserved in OgLuc. The distinct structural signature (inwhich an arginine or lysine, able to form a number of potential hydrogenbonds with the main chain carbonyls of a short 3₁₀ helix, packs across aconserved tryptophan in a structurally superimposable, non-randommanner) corresponds to sequence determinants common to the calycinmember families: a characteristic N-terminal sequence pattern,displaying preservation of key residues, and a weaker C-terminal motif.The preservation of particular residues and interactions, across themember families lends some support to the view that there was a common,if very distant, evolutionary origin for the calycin superfamily. Thepresent OgLuc model predicts that OgLuc residue Asn166 near theC-terminus is unable to hydrogen bond with main-chain carbonyls near theN-terminus. However, models of mutants containing either Arg or Lys atposition 166 suggest restoration of this structure motif could improvethe structural stability of the OgLuc and its expression/activity incells.

The invention will be further described by the following non-limitingexamples.

EXAMPLE 1

The shortcomings of OgLuc could be addressed by protein engineering, butto do so in an efficient manner would require knowledge about thethree-dimensional (3D) structure of OgLuc. There is no publishedexperimental tertiary structure or tertiary structure model of OgLuc.Homology modeling was used to generate a tertiary structure model ofOgLuc. Building a homology model comprises several steps includingidentification of 3D structural template(s), alignment of targetsequence (e.g., OgLuc) and template structure(s), model building, andmodel quality evaluation. Identification of one or more 3D structuraltemplates for OgLuc was not intuitive because standard sequence searchmethods did not identify significant overall similarity to proteins withknown tertiary structure. To overcome this problem, two approaches wereemployed to identify remote OgLuc homologs with known tertiarystructure.

Approach 1:

An Hidden Markov Model (HMM) based template library search (Karplus etal., Bioinformatics, 14:846 (1998)) was used to detect distantly relatedtemplate structures using the SWISS-MODEL Template Identification Toolat http://swissmodel.expasy.org//SWISS-MODEL.html (Arnold et al.,Bioinformatics, 22:195 (2006)).

The best (highest E-value score) 3D structure template identified forOgLuc using this approach was a fatty acid binding protein (FABP)(Protein Data Bank (PDB) accession number 1VYF) (Angelucci et al.,Biochemistry, 43:13000 (2004)). Additional FABPs with lower scores werealso identified, including PDB accession numbers 1PMP and 1CRB.

Exemplary alignments of the target sequence (OgLuc, residues 1-2 and168-169 omitted) and the sequences of the identified 3D structuretemplates (1VYF, 1PMP, 1CRB) are shown below. Note that due to the lowsequence similarity, the placement of gaps in the alignment can vary.

lvyf   1 GSMSSFLGKWKLSESHNFDAVMSKLGVSWATRQIGNTVTPTVTFTMDGDK..  50      F G W      N D V    G S      G  VTP       G Target   3--LADEVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENgl  52 1vyf  51.......MTMLTESTFKN..LSCTFKF.....................GEEF  72             S F        FK                      G Target  53kadihviIPYEGLSGFQMglIEMIFKVvypvddhhfkiilhygtividGVTP 104 1vyf  73DEKTSDGRNVKSVVEKNSESKLTQTQVDPKNTTVIVREV.DGDTMKTTVTVG 123      GR                      N     R           VT Target 105NMIDYFGRPYPGIAVFDGKQITVTGTLWNGNKIYDERLInPDGSLLFRVTIN 156 1vyf 124DVTAIRNYKRLS 135 (SEQ ID NO: 5)  VT  R Target 157 GVTGWRLCENI167 (SEQ ID NO: 7) 1pmp   3SNKFLGTWKLVSSENFDEYMKALGVGLATRKLGNLAKPRVIISKKGDI....  48   F G W      N D      G       LG    P       G Target   3LADEVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENglka  54 1pmp  49....................ITIRTESPFKNTEISFKL........GQEFEE  72                           P         L        G Target  55dihviipyeglsgfqmglieMIFKVVYPVDDHHFKIILhygtlvidGVTPNM 106 1pmp  73TTADNRKTKSTVTLARGSLNQVQK.WNGNETTIKRKL.VDGKMVVECKMKDV 122     R                   WNGN     R    DG          V Target 107IDYFGRPYPGIAVFDGKQITVTGT1WNGNKIYDERLInPDGSLLFRVTINGV 158 1pmp 123VCTRIYEKV 131 (SEQ ID NO: 3)    R  E Target 159 TGWRLCENI167 (SEQ ID NO: 7) 1crb   1PVDFNGYWKMLSNENFEEYLRALDVNVALRKIANLLKPDKEIVQDGDH....  48  DF G W      N    L                 P    V  G Target   3LADEVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENglka  54 1crb  49....................MIIRTLSTFRNYIMDFQV........GKEFEE  72                    MI                        G Target  55dihvilpyeglsgfqmglieMIFKVVYPVDDHHFKIILhygtividGVTPNM 106 1crb  73DLTGIDDRKCMTTVSWDGDKLQCVQK.GEKEGRGWTQWI.EGDELHLEMRAE 122       R          D        G          I     L Target 107--IDYFGRPYPGIAVFDGKQITVTGT1WNGNKIYDERLInPDGSLLFRVTIN 156 1crb 123GVTCKQVFKKVH 134 (SEQ ID NO: 4) GVT Target 157 GVTGWRLCENI-165 (SEQ ID NO: 7)

Approach 2:

A fold recognition method using the “GeneSilico meta-server” athttps://genesilico.pl/meta2 (Kurowski et al., Nucl. Acids Res., 31:3305(2003)) was also used to identify remote OgLuc homologs with knowntertiary structure.

A protein fold is a 3D structural classification. Proteins that sharethe same fold have a similar arrangement of regular secondary structuresbut without necessarily showing evidence of evolutionary relatedness onthe protein sequence level.

Using this method, three highest scoring 3D structure templates wereidentified (PDB accession numbers 1VYF, 1PMP, and 1CRB). Exemplaryalignments of the target sequence (OgLuc) and the sequences of the 3Dstructure templates (1VYF, 1PMP, 1CRB) are shown below. Note that due tothe low sequence similarity, the exact placement of gaps in thealignment is difficult to predict with confidence.

OgLuc and 1PMP:

--SNKFLGTWKLVSSENFDEYMKALGVGLATRKLGNLAKPRVIISKKG------DIITIRTE------------------FTLADFVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENGLKADIHVIIPYEGLSGFQMGLIEMIFKVV-----SPFKNTEISFKLGQEFEETTAD-----NRKTKSTVTLARGSLNQV-QKWNGNETTIKRKLV-DGKMVVECKMKDVYPVDDHHFKIILHYGTL--VIDGVTPNMIDYFGRPYPGIAVFDGKQITVTGTLWNGNKIYDERLINPDGSLLFRVTINGVVCTRIYEKV-- (1PMP) (SEQ ID NO: 3) TGWRLCENILA (OgLuc) (SEQ ID NO: 1)

OgLuc and FABPs:

--SNKFLGTWKLVSSENFDEYMKALGVGLATRKLGNLAKPRVIISKKG------DIITIRTESP------------------PVDFNGYWKMLSNENFEEYLRALDVNVALRKIANLLKPDKEIVQDG------DHMIIRTLST----------------GSMSSFLGKWKLSESHNFDAVMSKLGVSWATRQIGNTVTPTVTFTMDG------DKMTMLTEST----------------FTLADFVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENGLKADIHVIIPYEGLSGFQMGLIEMIFKVV-------FKNTEISFKLGQEFEETTA-----DNRKTKSTVTLAR-GSLNQV-QKWNGNETTIKRKLV-DGKMVVECKMKD-------FRNYIMDFQVGKEFEEDLT---GIDDRKCMTTVSWDG-DKLQCV-QKGEKEGRGWTQWIE-GDELHLEMRAEG-------FKNLSCTFKFGEEFDEKTS-----DGRNVKSVVEKNSESKLTQT-QVDPKNTTVIVREVD-GDTMKTTVTVGDYPVDDHHFKIILHYGTL--VIDGVTPNMIDYFGRPYPGIAVFDG-KQITVTGTLWNGNKIYDERLINPDGSLLFRVTINGVVCTRIYEKV-- (1PMP) (SEQ ID NO: 3) VTCKQVFKKVH- (1CRB) (SEQ ID NO: 4)VTAIRNYKRLS- (1VYF) (SEQ ID NO: 5) VTGWRLCENILA (OgLuc) (SEQ ID NO: 1)

Using the information generated in the above approaches, OgLuc homologymodels were generated based on three FABP 3D structure templates (1PMP,1CRB, and 1VYF) using Discovery Studio and MODELER software (AccelrysSoftware Inc.).

FIG. 1 also shows the secondary structure alignments of FABPs and OgLuc.1PMP, 1CRB, 1VYF are the Protein Data Bank (www.resb.org) accessioncodes for exemplary FABP sequences with known 3D structure. “PDB” meanssecondary structure assignment provided by authors who deposited the 3Dstructure information into Protein Data Bank. “DSC” means secondarystructure prediction based on DSC method (King et al., Protein Science,5:2298 (1996)). “Kabasch and Sander” means secondary structureprediction based on Kabasch and Sander method (Kabasch and Sander,Biopolymers, 22:2577 (198)). Red boxes indicate approximate extend ofhelix secondary structure elements, blue arrows indicate approximateextend of beta-sheet secondary structure elements, and gray barsindicate secondary structure other than helix or beta-sheet. Thesequence motifs centered on the conserved residues of the calycinstructural signature (Flower et al., Biochem. Biophys. Acta.,16:1088(2000)) may be seen in the alignments. The more highly conservedN-terminal MOTIF1 includes OgLuc residue Trp10, and the less wellconserved C-terminal MOTIF2 includes OgLuc residue N166. For the secondalignment, the approximate pair-wise percent protein sequence identitiesare: OgLuc-1PMP 14%, OgLuc-1CRB 9%, and OgLuc-1VYF 15%.

FIG. 2 shows the secondary structure alignments of dinoflagellateluciferase, FABP and OgLuc. 1VPR and 1HMR are the Protein Data Bank(www.resb.org) accession codes for sequences with known 3D structure.1VPR is dinoflagellate luciferase domain 3 and 1HMR is human muscleFABP, the most closely related protein to dinoflagellate luciferase(Schultz et al., PNAS USA, 102:1378 (2005)). “Kabasch and Sander” meanssecondary structure prediction based on Kabasch and Sander method(Kabasch and Sander, Biopolymers, 22:2577(1983)). Red boxes indicateapproximate extend of helix secondary structure elements, blue arrowsindicate approximate extend of beta-sheet secondary structure elements,and gray bars indicate secondary structure other than helix orbeta-sheet. 1VPR has SEQ ID NO:21; 1HMR has SEQ ID NO:22.

FIG. 3 shows the alignment of the amino acid sequences of OgLuc andvarious FABPs (SEQ ID NOs: 1, 3, 4, 5, and 17-20, respectively) based onthe 3D structure superimposition of FABPs.

EXAMPLE 2

Fatty acid binding proteins (FABPs) belong to the calycin proteinsuperfamily. Calycins have no significant overall similarity at thesequence level, but share a related beta-barrel structure with adistinct structural signature: an arginine or lysine (near theC-terminus) that is able to form a number of potential hydrogen bondswith the main chain carbonyls of a short 3₁₀ helix and packs across aconserved tryptophan (near the N-terminus) (Flower et al., Biochem.Biophys. Acta, 1482:9 (2000)). In the OgLuc model generated in Example1, the calycin structural signature is only partially present. Theconserved tryptophan (Trp10) near the N-terminus (such as one in aN-terminal beta-sheet of a beta-barrel) packs across an asparagine(Asn166) instead of an arginine or lysine near the C-terminus (such asone in a C-terminal beta-sheet of a beta-barrel). The present modelpredicts that the shorter asparagine side chain seems unable to formhydrogen bonds with residues near the N-terminus (in the N-terminalbeta-sheet of the beta-barrel). OgLuc models, where the substitutionsAsn166Arg and Asn166Lys were made, demonstrated that the longer arginineand lysine side chains in OgLuc should be able to form one or morebonds, e.g., one or more hydrogen bonds, with main chain carbonylsand/or side chains of residues near the N-terminus. For example, theymay form one or more hydrogen bonds with OgLuc residues Asp9 and/or Gly8and/or Asp5 near the N-terminus. Additionally, they could form one ormore hydrogen bonds to one or more residues in other secondary structureelements that are in close spacial proximity to position 166, e.g.,Asn144 and/or Glyl47. Thus, restoring the calycin structural signaturein OgLuc with an Asn166Arg or Asn166Lys mutation may effectively tietogether the two termini of the beta-barrel (or terminal beta-sheets ofthe beta-barrel) and possibly other secondary structure elements. Thiscould improve overall stability of the protein structure, and thus OgLucactivity.

An exemplary OgLuc protein sequence is

FTLADFVGDW QQTAGYNQDQ VLEQGGLSSL FQALGVSVTPIQKVVLSGEN GLKADIHVII PYEGLSGFQM GLIEMIFKVVYPVDDHHFKI ILHYGTLVID GVTPNMIDYF GRPYPGIAVFDGKQITVTGT LWNGNKIYDE RLINPDGSLL FRVTINGVTG WRLCE NILA (SEQ ID NO: 1; 169 amino acids, Asn166 bold underlined).

An exemplary OgLuc nucleotide sequence is

(SEQ ID NO: 2) atggtgtttaccttggcagatttcgttggagactggcaacagacagctggatacaaccaagatcaagtgttagaacaaggaggattgtctagtctgttccaagccctgggagtgtcagtcaccccaatccagaaagttgtgctgtctggggagaatgggttaaaagctgatattcatgtcatcatcccttacgagggactcagtggttttcaaatgggtctgattgaaatgatcttcaaagttgtttacccagtggatgatcatcatttcaagattattctccattatggtacactcgttattgacggtgtgacaccaaacatgattgactactttggacgcccttaccctggaattgctgtgtttgacggcaagcagatcacagttactggaactctgtggaacggcaacaagatctatgatgagcgcctgatcaacccagatggttcactcctcttccgcgttactatcaatggagtcaccggatggcgcctttgcga gAACattcttgcc.

The AAC codon of SEQ ID NO:2, which is capitalized in the listing above,corresponds to amino acid position 166 in the mature wild-type OgLucsequence of SEQ ID NO:1. The nucleotide sequence of SEQ ID NO:2 alsoincludes an ATG codon (methionine/start signal) and a GTG codon (valine)at the beginning for convenience of use in expression systems.Nevertheless, the amino acid numbering used throughout this applicationto identify substituted residues is given relative to the maturewild-type OgLuc polypeptide sequence of SEQ ID NO:1. Thenaturally-occurring wild-type OgLuc sequence may be initiallysynthesized with other amino acids which are later cleaved, resulting inthe generation of a mature wild-type polypeptide such as shown in SEQ IDNO:1. For example, a signal sequence (e.g. to direct the nascent proteinto a particular organelle such as the endoplasmic reticulum and/or todirect the protein for secretion) may be present at the beginning of thenascent protein and may then be cleaved to produce the mature wild-typeprotein.

An exemplary alignment of OgLuc and three FABPs is shown below.

--SNKFLGTWKLVSSENFDyYMKALGVGLATRKLGNLAKPRVIISKKG------DIITIRTESP------------PVDFNGYWKMLSNENFEEYLRALDVNVALRKIANLLKPDKEIVQDG------DHMIIRTLST----------GSMSSFLGKWKLSESHNFDAVMSKLGVSWATRQIGNTVTPTVTFTMDG------DKMTMLTEST----------FTLADFVGDWQQTAGYNQDQVLEQGGLSSLFQALGVSVTPIQKVVLSGENGLKADIHVIIPYEGLSGFQMGLIE          11               33              44        54-------------FKNTEISFKLGQEFEETTA-----DNRKTKSTVTLAR-GSLNQV-QKWNGNETTIKRKLV--------------FRNYIMDFQVGKEFEEDLT---GIDDRKCMTTVSWDG-DKLQCV-QKGEKEGRGWTQWIE--------------FKNLSCTFKFGEEFDEKTS-----DGRNVKSVVEKNSESKLTQT-QVDPKNTTVIVREVD-MIFKVVYPVDDHHFKIILHYGTL--VIDGVTPNMIDYFGRPYPGIAVFDG-KQITVTGTLWNGNKIYDERLINP75                             114        115       124        135DGKMVVECKMKDVVCTRIYEKV-- (SEQ ID NO: 3) GDELHLEMRAEGVTCKQVFKKVH-(SEQ ID NO: 4) GDTMKTTVTVGDVTAIRNYKRLS- (SEQ ID NO: 5)KRSLLFRVTINGVTGWRLCENILA (SEQ ID NO: 1)

EXAMPLE 3

Generation of Modified Luciferase Variants with Increased Luminescence

Unless otherwise stated, variants of a starting OgLuc sequence withrandom substitutions were generated using the error-prone, mutagenicPCR-based system GeneMorph II Random Mutagenesis Kit (Stratagene;Daughtery, PNAS USA 97(5):2029 (2000)), according to manufacturer'sinstructions, and NNK saturation as known in the arts. The resultingvariants were constructed in the context of pF1K Flexi® vector for T7based expression (Promega Corp.) and were used to transform KRX E. coliusing techniques known in the art. The resulting library was expressedin E. coli and screened for variants that had increased light emissioncompared to the starting OgLuc protein. Standard sequencing techniquesknown in the art were used to identify the amino acid substitution ineach clone of interest.

Variants of a starting OgLuc sequence with specific mutations weregenerated using the oligo-based site-directed mutagenesis kit QuikChangeSite-Directed Mutagenesis Kit (Stratagene; Kunkel, PNAS USA 82(2):488(1985)), according to the manufacturer's instructions.

EXAMPLE 4

Methods to Measure Light Emission and Signal Stability

E. coli clones containing the plasmid DNA encoding modified luciferasevariants with amino acid substitutions in OgLuc were grown in a 96-wellplate and induced with walk away induction, i.e. autoinduction (Shagatet al., “KRX Autoinduction Protocol: A Convenient Method for ProteinExpression,” Promega Notes 98:17 (2008)) for 17 hours. Each variant andcorresponding starting luciferase had 6 well replicates. Cells werelysed using a lysis buffer consisting of 150 mM HEPES pH 8.0, 100 mMthiourea, 0.1× PLB (Promega Corp. Cat. No. E194A), 0.1 mg/mL lysozymeand 0.001 U/μL RQ1 DNase, and measured for luminescence using Renillaluciferase substrate reagents (Promega Corp.) on an Infinite 500 Tecanluminometer. Measurements were taken immediately after addition withinjection of either a “Glo” 0.5% tergitol assay buffer (“0.5%tergitol”), which contains 150 mM KCl, mM CDTA, 10 mM DTT, 0.5%tergitol, 20 μM coelenterazine (Promega Corp.)), or a “Flash” RLABbuffer (Promega Corp.) containing 20 μM coelenterazine (Promega Corp.)(“RLAB”) to the lysate sample. This luminescence measurement, takenimmediately after addition, is the “T=0” time point measurement and invarious embodiments is taken as a measure of the total light output(luminescence) generated by the sample. The average luminescence of the6 replicates was compared between the variants with that of thecorresponding starting luciferase. In various embodiments, theluminescence measurements were normalized to the corresponding startingluciferase of interest, for example synthetic OgLuc, and referred to incertain embodiments as “fold” (i.e. 2-fold, 3-fold, 4.5-fold, etc.)improvement, increase, or the like.

The signal stability of a variant clone was determined by re-reading theplate multiple times after the addition of the assay buffer to thesample, for example, measuring luminescence every 30 seconds or every 1minute, for a length of time. The signal half-life was determined usingthese measurements and the average of the 6 replicates was comparedbetween the variants with the corresponding starting luciferase. Thehalf-life indicating signal stability was normalized to thecorresponding starting luciferase of interest, for example OgLuc.

EXAMPLE 5

Method of Measuring Protein Stability, i.e. Thermostability

Lysate samples were prepared from induced cultures as described inExample 4. Lysate samples in replicate 96 well plates were incubated atvarious temperatures, including for example at 22, 30, 37, 42, 50 or 54°C. At different time points, plates were placed at −70° C. Prior tomeasuring the luminescence as described in Example 4, each plate wasthawed at RT, i.e. 22° C., for 10 minutes. Samples were assayed with the0.5% tergitol assay buffer described in Example 4. The “T=0”measurement, as described in Example 4, for each time point plate, wasused to determine the half-life of the protein. The half-life, whichindicates protein stability, was normalized to the correspondingstarting luciferase of interest, for example OgLuc.

EXAMPLE 6

Generation of a Modified Luciferase with Increased Light Emission

To examine whether restoring the calycin structural signature in OgLuccould improve overall protein stability and activity, synthetic versionsof the OgLuc sequence was designed. The synthetic versions includedoptimized codon usage for E. coli and mammalian cells and codons foreither Arg or Lys substituted for Asn at position 166. As mentionedpreviously, the numbering is based on SEQ ID NO:1. Codon optimization(for E. coli ) and nucleotide changes for codon 166 to Arg or Lys wereengineered by synthetic means (Gene Dynamics, LLC). In the cloneOgLuc+N166R, the AAC codon was changed to CGT (to code for Arg). In theclone OgLuc+N166K, the AAC codon was changed to AAA (to code for Lys).

The synthetic OgLuc genes were subcloned into a vector suitable foroverexpression in bacteria or TnT® rabbit reticulocyte lysates (PromegaCorp.; pF1K Flexi® vector for T7 based expression systems), and used totransform KRX E. coli. Individual colonies were picked, grown, inducedwith rhamnose, lysed using lysozyme and a single freeze-thaw, andmeasured for luminescence using Renilla luciferase substrate reagents(Promega Corp.) on a Veritas luminometer. Rabbit reticulocyte TnT®reactions were carried out according to the manufacturer's protocols(Promega Corp.) and measured the same way as the bacterial lysates.

The mutants were compared to the synthetic parental (i.e. starting)OgLuc protein for production of total light output (luminescence). In E.coli, a 5-fold and 10-fold improvement (N166K and N166R, respectfully)in luminescence was observed with coelenterazine as a substrate. In theTnT® lysates the improvement was between 4-fold and 7-fold (N166K andN166R). These sequences (containing either Arg or Lys at position 166)represent variants of OgLuc that result in enhanced stability.

Various OgLuc variants with an amino acid substitution at position 166were analyzed for brightness, e.g., screened for variants that were atleast 1.2× brighter than wild type OgLuc. The following substitutionsyielded a variant that was at least 1.2× brighter than wild type OgLuc:N166K; N166R; N166A; N166L; N166P; N166Q; and N166S. (See Table 1).Table 1 shows the brightest variant, as indicated by the foldimprovement over wild-type OgLuc, had the amino acid substitution N166R.

TABLE 1 Summary of the fold improvement in luminescence of the OgLucvariants with amino acid substitution at position 166 over wild typeOgLuc. Amino Acid Substitution at Position 166 Fold improvement R 10 K 4A 3 L 3 P 2 Q 2 S 2

Mutagenesis using error-prone PCR and NNK saturation, as described inExample 3, of the OgLuc+N166R variant resulted in variants with enhancedbrightness, e.g., at least 1.2× brighter, relative to the OgLuc+N166Rvariant. Table 2 summarizes these variants which comprised the N166Rsubstitution as well as one of the following substitutions at residues 2(S), 4 (E, S, R, G, D, T or L), 11 (R, V, I, L, K or T), 33 (K), 44 (Ior L), 45 (E), 54 (F, T, V, G, W, S, or L), 68 (V, Y),75 (R, K, Q, G, Tor A), 104 (L), 115 (E, I, Q, L, V, G, H, R, S, C, A, or T), 124 (K),135 (K), 138 (V, I, N, T, L, C, R, M or K), 139 (E), 167(V), or 169 (L).Table 2 shows the fold improvement in luminescence fold-improvement ofthe variant over the corresponding starting OgLuc+N166R variant usingRLAB using an average of the signal in the range of 4-6 minutes afterstarting the reaction, e.g. after injection of the substrate. For eachamino acid substitution listed, the most improved substitution is listedfirst and the least improved substitution listed last. The variantswhich showed the most improvement included variants containing asubstitution at residue 4, 54, or 138.

TABLE 2 Summary of the fold improvement in luminescence of the OgLuc +N166R variants over the corresponding starting OgLuc + N166R.Fold-improved brightness Amino (RLAB), 4-6 min average Position acidCodon (rel. to N166R)   2 S TCC  9   4 E GAG 20   4 S AGT  7   4 R AGG 6   4 G GGG  4   4 D GAT  4   4 T ACG  3   4 L CTG  3  11 R CGG 13  11V GTG  6  11 I ATT  6  11 L CTT  3  11 K AAG  3  11 T ACT  2  33 K AAG10  44 I ATT 25  44 L CTT  2  45 E GAG  2  54 F TTT 10  54 T ACT  8  54V GTT  6  54 G GGG  5  54 S AGT  4  54 W TGG  3  54 L TTG  2  68 V GTT 2  68 Y TAT  3  72 Q CAG  3  75 R AGG  6  75 K AAG  5  75 Q CAG  5  75G GGT  4  75 T ACG  4  75 A GCG  4 104 L CTT 10 115 E GAG 20 115 I ATT 4 115 Q CAG  3 115 L CTT  3 115 V GTT  3 115 G GGG  3 115 H CAT  3 115R CGG  2 115 S AGT  2 115 C TGT  2 115 A GCT  2 124 K AAA  8 135 K AAG10 138 V GTG 10 138 I ATT  8 138 T ACG  6 138 L CTG  5 138 C TGT  6 138R CGG  5 138 M ATG  4 138 K AAG  3 139 E GAG 13 167 V GTT 40 169 L TTG10

Additional variants of the OgLuc+N166R variant had more than one aminoacid substitution. These additional variants are listed in Table 2 withthe amino acid substitutions listed and the fold improvement inluminescence of the OgLuc+N166R variant over the corresponding startingN166R OgLuc. Additional variants were found which included silentmutations, i.e. changes in nucleotides which did not alter the aminoacid encoded at that codon.

TABLE 3 Summary of the fold improvement in luminescence of theOgLuc+N166R variants with more than one amino acid substitution and/orsilent mutations over the corresponding starting OgLuc+N166R. Fold overAmino Acid change from N166R N166R (codons) 6 E23V (gta), S28P (cct),I143V (ctc) 15 A4S (gca), L34M (atg), I76V (gtc) 2 G51V (gtt), I99V(gtt) 13 L3L (tta), S37S (tcg), V44V (gta) 5 L3L (tta), L27M (atg) 5 L3L(tta) 4 L3L (tta), Q32L (cta), K43R (aga) 3 L72Q (cag), G10G (ggt) 2N144K (aag), A54A (gca)

EXAMPLE 7

Evaluation of Specific Substitutions in Modified Luciferases

Additional OgLuc variants were generated by site-directed mutagenesis asdescribed in Example 3 to have a substitution at one of the followingpositions: 2, 4, 11, 44, 54, 90, 115, 124 or 138 relative to SEQ IDNO:1. Substitutions at these positions in combination with N166R, wereshown in Example 6 to have increased total light output (luminescence)compared to WT OgLuc. In FIGS. 5A-5C, 6A-6C, 7A-7C, 8, 9A-9D, 10A-10C,11A-11B, 12A-12B and 33A-33E, “WT,” “N166R,” and “T2T” refer to theproteins encoded by SEQ ID NOS:2, 14 and 32, respectfully, “T2T+N166R”refers to the protein encoded by SEQ ID NO:32, which has a substitutionat N166R, “A4E,” “Q11R,” “V44I,” “A54F,” “A54F+N166R,” “A54I,” “P115E,”“P155E+N166R,” “Y138I,” “Q124K,” “Y138C+N166R,” and “I90V” each refer tothe protein encoded by SEQ ID NO:2 having a substitution at therespective residues indicated in the “Sample” column in FIG. 5A. Thesevariants were evaluated by measuring the luminescence as described inExample 4. FIGS. 5A-5C and 7A-7C summarize the average luminescence atT=0 of the WT OgLuc variants using either 0.5% tergitol (FIG. 5A-5C) orRLAB (FIG. 7A-7C). The fold increase in luminescence of the variantsover WT OgLuc is shown in FIGS. 6A-B (0.5% tergitol) and FIG. 8 (RLAB).The fold increase in luminescence of the variants over the N166R variantis shown in FIGS. 33A (0.5% tergitol) and 33B (RLAB). FIGS. 5B, 6B, and7B show the same data as FIG. 5C, 6C, and 7C, respectively, but atdifferent scales to permit the smaller bars to be seen more clearly.

To determine if the amino acid substitutions in the different variantsalso had an effect on signal stability, the signal stability wasmeasured for each variant. The signal stability of the variants wasmeasured as described in Example 4 and shown in FIG. 9A-9C (0.5%tergitol) and FIGS. 10A-10C (RLAB) as the total light output(luminescence) over time. The signal half-life of each variant wasdetermined from this data and shown in FIG. 9D (0.5% tergitol) and FIGS.11A-11B (RLAB). The signal half-life for each variant was normalized tothe N166R variant and shown in FIG. 33C.

To determine if the amino acid substitutions in the different variantsalso had an effect on protein stability (i.e. thermostability), theprotein stability of each variant at 22° C. was measured as described inExample 5 and shown in FIGS. 12A-12B. At 22° C., the OgLuc A54F+N166Rvariant protein had a half-life of 178 minutes, while the OgLucP115E+N166R variant had a half-life of almost 120 minutes, compared toWT OgLuc, which had a half-life of 38 minutes.

FIG. 33D summarizes the half-life in minutes at 22° C. of the OgLucvariants compared to WT OgLuc shown in FIGS. 12A-B and 17 normalized tothe N166R variant.

FIG. 33E summarizes the increase fold in luminescence, signal half-lifeand half-life at 22° C. shown in Figures A-D.

EXAMPLE 8

Evaluation of Specific Substitutions in Modified Luciferases

Additional synthetic OgLuc variants were generated with substitutions atsites 33 and 68. Specifically, A33K and F68Y substitutions were made inWT OgLuc (identified as “WT A33K” and “WT F68Y” in FIGS. 13A-13B,14A-14B, 15A-15B, 16A-16B, 17, and 33A-33E) and the OgLuc+N166R(identified as “N166R A33K” and “N166R F68Y” in FIGS. 13A-13B, 14A-14B,15A-15B, 16A-16B, 17, and 33A-33E) variant sequence and compared withthe corresponding starting WT OgLuc (identified as “WT” in FIGS.13A-13B, 14A-14B, 15A-15B, 16A-16B, 17, and 33A-33E) and OgLuc+N166Rvariant (identified as “N166R” in FIGS. 13A-13B, 14A-14B, 15A-15B,16A-16B, 17, and 33A-33E). The average luminescence at T=0 of the OgLucA33K and F68Y variants using 0.5% tergitol and RLAB are shown in FIG.13A and 13B, respectively. The A33K and F68Y variants had higherluminescence compared to the respective corresponding starting OgLuc asfurther shown with the fold increase in luminescence of the variantsover the WT OgLuc in FIGS. 14A (0.5% tergitol) and 14B (RLAB). A33K andF68Y separately in the wild-type background showed 1.6 and 1.7 foldincrease over WT using RLAB (see FIG. 14B) and 3.8 and 3.9 fold increaseover WT 0.5% tergitol (FIG. 14A). A33K and F68Y separately in theOgLuc+N166R background showed 5.1 and 3.3 fold increase over WT OgLucusing RLAB (see FIG. 14B) and 9.2 and 5 fold increase over WT OgLucusing 0.5% tergitol (FIG. 14A).

The fold increase in luminescence of the variants over the OgLuc+N166Rvariant is shown in FIGS. 33A (RLAB) and 33B (0.5% tergitol). Thesubstitution A33K in the wild-type background showed 2.6 (0.5%tergitol)and 0.6 (RLAB) fold increase in luminescence over the OgLuc+N166Rvariant. (see FIG. 33A and 33B). The substitution F68Y in the wild-typebackground showed 2.7 (0.5% tergitol) and 0.7 (RLAB) fold increase overthe OgLuc+N166R variant (see FIG. 33A and 33B). The substitution A33K inthe OgLuc+N166R variant background showed 6.3 (0.5% tergitol) and 2.0(RLAB) fold increase over the OgLuc+N166R variant (see FIGS. 33A and33B). The substitution F68Y in the OgLuc+N166R background showed 3.4(tergitol) and 1.3 (RLAB) fold increase over N166R (see FIG. 33A and33B).

The signal stability of the A33K and F68Y variants was measured asdescribed in Example 4 using 0.5% tergitol (FIGS. 15A-15B) and RLAB(FIGS. 16A-16B). The signal half-life of the A33K variant in the WTOgLuc background was higher than the WT OgLuc half-life, but lower inthe OgLuc+N166R variant background when using either 0.5% tergitol (FIG.15B) or RLAB (FIG. 16B). The signal half-life of the F68Y variant in theWT OgLuc background was higher than the WT OgLuc half-life using 0.5%tergitol (FIG. 16B), but lower in either background using RLAB (FIG.15B).

The protein stability (i.e. thermostability) of the A33K and F68Yvariants was measured as described in Example 5 at 22° C. and shown inFIG. 17. The A33K and F68Y substitutions in the N166R variant backgroundhad a longer half-life, specifically 72 and 78 minutes compared to WTOgLuc and the N166R variant, which was 55 and 67 minutes, respectively(FIG. 17). The A33K and F68Y substitutions in the WT OgLuc background,had 58 and 57 minutes half-lives, respectively (FIG. 17).

EXAMPLE 9

Evaluation of Specific Core Combinations of Substitutions in ModifiedLuciferases—Light Emission

To determine if a combination of two or more amino acid substitutions inOgLuc provides a further improvement in luminescence, different variants(designated C1-C3) of OgLuc were generated containing the followingamino acid substitutions: Cl: N166R, Q11R, A33K, A54F, P115E, Q124K,Y1381 and V441 (residue 44 may come into contact with substrate), C2:V45E, N135K, I167V, P104L, and D139E (note that 2 of these are at sitesthat may come into contact with substrate); C3; S28P, L34M, G51V, I99V,and I143L. These Core Combination variants were generated by mutatingthe T2T OgLuc by site-directed mutagenesis as described in Example 3.The Cl variant was further mutated to contain an A4E amino acidsubstitution to create the C1+A4E variant. Combinations of thesevariants were also created with the A4E substitutions, e.g., C1+C2+A4Eand C1+C330 A4E. These recombinant clones were constructed usingoligonucleotide-based site-directed mutagenesis followed by subcloninginto pF4Ag vector (contains T7 and CMV promoters; commercially-availablepF4A modified to contain an E. coli ribosome-binding site). All variantswere screened in E. coli cells. Briefly, clones were overexpressed inKRX E. coli, after which cells were lysed and measured for luminescenceusing colenterazine as a substrate. The OgLuc N166R variant and Renillaluciferase were also screened. Both C1, C1+A4E and C1+C3+A4E variantswere approximately 4 logs brighter than the OgLuc N166R variant and atleast as bright as Renilla luciferase (FIG. 4A-4D). The total lightoutput (i.e. luminescence) of these Core Combination variants at T=0 wasmeasured as described in Example 4 using the “Flash” 0.5% tergitol (FIG.4A) and the “Glo” RLAB (FIG. 4B).

An alignment of the protein (FIG. 31) and nucleotide (FIG. 32) sequencesof the native, WT, N166R, C1, C1+C2, C1+A4E, C1+C2+A4E, and C1+C3+A4E isshown.

An additional substitution was introduced into C1+A4E and C1+C3+A4E.Specifically, the A54F residue in these variants was changed to F54T.These variants, C1+A4E+F54T and C1+C3+A4E+F54T, were compared to thecorresponding starting C1+A4E and C1+C3+A4E, as well as Renilla and WTOgLuc luciferases using the method of Example 4. As seen in FIGS. 18A,18B and 19, the variants with the F54T substitution had a 50-75%decrease with 0.5% tergitol and about 2-5 fold increase in luminescencewith RLAB compared to WT (see T=0 measurement in FIGS. 18A and 19,respectfully). The addition of the F54T substitution showed increasedtotal light output with RLAB, but showed a faster decay over time (FIG.19). With 0.5% tergitol, the decay over time is similar to C1+A4E, butthe RLU's are lower compared to C1+A4E (FIG. 18A-18B).

The luminescence of the C1, C1+A4E, C1+C2, and C1+C2+A4E variants, ascompared with Renilla luciferase, WT OgLuc, T2T and the A54F variant,was measured using the method described in Example 4. (FIG. 20A and20B). The C1+A4E and C1+C2+A4E variants had 4 and 2-log increase,respectfully, over WT using 0.5% tergitol (FIG. 20A). The C1+A4E,C1+C2+A4E, and C1+C3+A4E variants had 3, 1.5, and 3-log increase,respectfully, over WT using RLAB (FIG. 20B). A 0.25% tergitol buffer wasused instead of 0.5% tergitol to determine the stability of the signal,not reliant on tergitol. FIG. 21 shows the C1, C1+A4E, C1+C2, andC1+C2+A4E variants having 4, 4, 2, and 2-log increase, respectfully,over WT using 0.25% tergitol.

The C1, C1+A4E, C1+C2, and C1+C2+A4E variants, as compared with Renillaluciferase, WT OgLuc, T2T and OgLuc+A54F variants, were also evaluatedin HEK 293 cells. Briefly, HEK293 cells, plated at 15,000 cells/well ina 96-well plate, were transiently transfected using TranslT-LTI (minisBio) with plasmid DNAs encoding the various variants and/or controlsequences. The same plasmids also carried a gene for constitutiveexpression of firefly luciferase to act as a transfection control.Briefly, cells were grown, lysed and treated as described in Example 4.Cells were co-transfected with pGL4.13 for firefly transfection control(used 0.04 ug/tranfection or 10% of the total DNA transfected).Luminescence was measured as described in Example 4 using RLAB (FIG. 22)or 0.25% tergitol (FIG. 23). All modified luciferase data was thennormalized for transfection efficiency using firefly luciferaseluminescence (luciferin substrate) (FIGS. 22 and 23). The C1, C1+A4E,C1+C2, and C1+C2+A4E variants all had greater luminescence compared toOgLuc in 0.5% tergitol (FIG. 22). The C1+A4E and C1+C2+A4E variants alsohave greater luminescence compared to OgLuc in 0.25% tergitol (FIG. 23).

EXAMPLE 10

Evaluation of Specific Combinations of Substitutions in ModifiedLuciferases—Protein Stability

To determine if the amino acid substitutions in the different variantsalso had an effect on protein stability, the different variants werescreened at different temperatures, and the effect on stabilitymeasured. As shown in FIG. 24, at room temperature (about 22° C.), thewild-type OgLuc showed a protein half-life of 1 hour while the C1variant showed a protein half-life of 9.4 hours. As shown in FIG. 24, at30° C., the OgLuc N166R variant had a protein half-life of 21 minuteswhile the C1+A4E variant showed now decay after 6 hours. At 30° C., theprotein half-life for Renilla luciferase was 7.9 hours. The stabilityranking at 30° C. is OgLuc C1+A4E>Renilla luciferase>OgLuc N166R. Asshown in FIG. 24, at 37° C., the protein half-life of the OgLuc N166Rvariant was 2 minutes while no decay was seen in the C1+A4E variant. At54° C., the protein half-lives of the different variants were asfollows: C: 7 minutes, C1+A4E: 8 minutes, C1+C2+A4E: 128 minutes, andC1+C3+A4E: 24 minutes. The half-lives of wild-type OgLuc and OgLuc N166Rvariant could not be determined at 54° C. because they were toounstable.

EXAMPLE 11

Evaluation of Specific Combinations of Substitutions in ModifiedLuciferases—Signal Stability

To determine if the amino acid substitutions in the different variantsalso had an effect on signal stability, the different variants werescreened for signal stability. Signal stability was measured asdescribed in Example 4 using RLAB. The following signal half-lives weredetermined for the different variants: wild-type OgLuc:1.8 minutes,Renilla luciferase: 0.8 minutes, C1: 1.7 minutes, C1+A4E: 1.7 minutes,C1+C2+A4E: 12.6 minutes, and C1+C3+A4E: 3.3 minutes (FIG. 25).

EXAMPLE 12

Evaluation of Specific Combinations of Substitutions in ModifiedLuciferases—Luminescence Color

The optimal wavelength with the greatest luminescence usingcoelenterzaine (Promega Corp.) as substrate was determined for theOgLuc+N166R, C1+A4E and C1+C2+A4E variants, compared with Renillaluciferase. Samples were prepared as described in Example 4. Thespectral peak was determined by measuring the luminescence at 5 nmincrements in wavelength using a Varioskan luminometer and 0.5%tergitol. The data was normalized by the highest RLU value in thespectrum. As shown in FIG. 26, Renilla has a spectral peak of 480 nm,while OgLuc+N166R, C1+A4E and C1+C2+A4E have a spectral peak at 465 nm,which is a shift from native OgLuc, which was previously reported to be455 nm (Inouye, FEBS Letters, 481(1):19-25 (2000)).

EXAMPLE 13

Generation of a Modified Luciferase with Increased Luminescence

Additional variants were generated by random mutagenesis as described inExample 3 of the C1+A4E variant. The total light output was measured asdescribed in Example 4. Exemplary C1+A4E variants (i.e. those that areat least 1.2 times brighter than C1+A4E), but are not limited to, arelisted in FIG. 27A and 27B by Sample ID and the amino acid substitution.C1+A4E variants with an amino acid substitutions at positions 20, 54,72, 77, 79, 89, 90, or 164 relative to SEQ ID NO: 1, showed at least 1.9fold increase in luminescence over the corresponding starting C1+A4Evariant.

Clone 29H7, which contained the C1+A4E+F54I variant was further testedfor protein stability at 50° C. using the method described in Example 5.Clone 29H7 had a longer half-life than the corresponding starting C1+A4Evariant (FIG. 30).

Various C1+A4E variants with an amino acid substitution at position 92were analyzed for brightness, e.g., screened for variants that were atleast 1.2 times brighter than C1+A4E variant. The followingsubstitutions yielded a variant that was at least 1.2 times brighterthan C1+A4E: L92G; L92Q; L92S; and L92A, and had 2.2, 2, 2.9 and 2.5fold increase over C1+A4E respectively (see FIG. 28).

Additional variants were generated by site-directed mutagenesis,described in Example 3, of the C1+A4E variant, to have specificcombinations of the substitutions F541, F68S, M75K and I90V. As shown inFIG. 29, which lists the variants (“Sample ID”) and the amino acidsubstitutions found in each variant, these combinations of substitutionsshow significant increase in luminescence of at least 17.5-19.3 foldover the corresponding starting C1+A4E variant.

All publications, patents and patent applications are incorporatedherein by reference. While in the foregoing specification, thisinvention has been described in relation to certain preferredembodiments thereof, and many details have been set forth for purposesof illustration, it will be apparent to those skilled in the art thatthe invention is susceptible to additional embodiments and that certainof the details herein may be varied considerably without departing fromthe basic principles of the invention. An additional specificcombination variant of C1+A4E, was generated to include 190V and F54I(“IV”). As shown in FIG. 34A, IV had about 20 fold increase inluminescence compared to the corresponding starting C1+A4E variant asmeasured using the method of Example 4. As shown in FIG. 34B, the IVprotein was more stable than Renilla luciferase at 50° C. as thehalf-life for IV was 27.2 minutes compared to Renilla which was 9.6minutes using the method of Example 5.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A polynucleotide encoding a modified luciferase polypeptide having at least 60% amino acid sequence identity to a wild-type Oplophorus luciferase comprising at least one amino acid substitution at a position corresponding to an amino acid in a wild-type Oplophorus luciferase of SEQ ID NO:1, wherein the modified luciferase polypeptide has at least one of enhanced luminescence, enhanced signal stability, and enhanced protein stability relative to the wild-type Oplophorus luciferase.
 2. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide has enhanced luminescence relative to the wild-type Oplophorus luciferase and an amino acid substitution at at least one of positions 2, 4, 11, 20, 23, 28, 33, 34, 44, 45, 51, 54, 68, 72, 75, 76, 77, 89, 90, 92, 99, 104, 115, 124, 135, 138, 139, 143, 144, 164, 166, 167, or 169 corresponding to SEQ ID NO:1.
 3. The polynucleotide of claim 1, wherein the modified luciferase polypeptide has enhanced signal stability relative to wild-type Oplophorus luciferase, and an amino acid substitution at at least one of positions 4, 11, 20, 28, 33, 54, 68, 75, 115, 124, 138, 143, or 166, corresponding to SEQ ID NO:1.
 4. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide has enhanced protein stability relative to wild-type Oplophorus luciferase, and an amino acid substitution at at least one of positions 11, 20, 28, 33, 34, 44, 45, 51, 54, 68, 72, 75, 77, 89, 90, 92, 99, 104, 115, 124, 135, 138, 139, 143, 144, 164, 166, 167, or 169 corresponding to SEQ ID NO:1.
 5. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide further comprises a deletion of luciferase residues corresponding to the N-terminus of the wild-type Oplophorus luciferase of SEQ ID NO:10.
 6. The polynucleotide of claim 5, wherein the deletion is at most 27 residues of the luciferase sequence.
 7. The polynucleotide of claim 1, wherein the wild-type Oplophorus luciferase is from Oplophorus gracilirostris, Oplophorus grimaldii, Oplophorus spinicauda, Oplophorus foliaceus, Oplophorus novaezelandiae, Oplophorus typus, or Oplophorus spinous.
 8. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide comprises a substitution corresponding to at least one of T2S, A4E/S/R/G/D/T/L, Q11R/V/I/L/K/T, Q20R, E23V, S28P, A33K, L34M, V44I/L, V45E, G51V, A54F/TN/G/S/W/L/I, F68S/Y/V, L72Q, M75R/K/Q/G/T/A, I76V, F77W, V79I, K89E, I90TN, L92S/A/G/Q, I99V, P104L, P115E/I/Q/L/V/G/H/R/S/C/A/T, Q124K, N135K, Y138V/I/N/T/L/C/R/M/K, D139E, I143L, N144K, C164S, N166R/K/A/L/P/Q/S, I167V, or 169L corresponding to SEQ ID NO:1.
 9. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide comprises amino acid substitutions at positions 11, 33, 44, 54, 115, 124, 138, and 166 corresponding to SEQ ID NO:.
 10. The polynucleotide of claim 9, wherein the substitutions comprise Q11R, A33K, V44I, A54F, P115E, Q124K, Y138I, and N166R.
 11. The polynucleotide of claim 9, wherein the encoded modified luciferase further comprises an amino acid substitution at position 4 corresponding to SEQ ID NO:1.
 12. The polynucleotide of claim 11, wherein the amino acid at position 4 is glutamic acid.
 13. The polynucleotide of claim 9, wherein the encoded modified luciferase further comprises amino acid substitutions at positions 45, 135, 104, 139, and 167 corresponding to SEQ ID NO:1.
 14. The polynucleotide of claim 13, wherein the amino acid at position 45 is glutamic acid, position 104 is leucine, position 135 is lysine, position 139 is glutamic acid, and position 167 is valine.
 15. The polynucleotide of claim 11, wherein the encoded modified luciferase further comprises amino acid substitutions at positions 28, 34, 51, 99 and 143 corresponding to SEQ ID NO:1.
 16. The polynucleotide of claim 15, wherein the amino acid at position 28 is proline, position 34 is methionine, position 51 is valine, position 99 is valine, and position 143 is leucine.
 17. The polynucleotide of claim 11, further comprising a substitution of at least one amino acid at position 20, 54, 68, 72, 77, 79, 89, 90, 92, or 164 corresponding to SEQ ID NO:1.
 18. The polynucleotide of claim 17, wherein the amino acid at position 20 is arginine, position 54 is isoleucine, position 68 is serine, position 72 is glutamine, position 75 is lysine, position 77 is tryptophan, position 79 is isoleucine, position 89 is glutamic acid, position 90 is threonine or valine, position 92 is glycine, glutamine, serine or alanine, and position 164 is serine.
 19. The polynucleotide of claim 11, wherein the encoded modified luciferase polypeptide comprises amino acid substitutions at positions 23, 28, 143, and 166 corresponding to SEQ ID NO:1.
 20. The polynucleotide of claim 19, wherein the substitutions comprise E23V, S28P, I143V, and N166R.
 21. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide comprises amino acid substitutions at positions 4, 34, 76, and 166 corresponding to SEQ ID NO:1.
 22. The polynucleotide of claim 21, wherein the substitutions comprise A4S, L34M, I76V, and N166R.
 23. The polynucleotide of claim 1, wherein the encoded modified luciferase polypeptide comprises amino acid substitutions at positions 51, 99, and 166 corresponding to SEQ ID NO:1.
 24. The polynucleotide of claim 23, wherein the substitutions comprise G51V, I99V, and N166R.
 25. The polynucleotide of claim 1, wherein the polynucleotide further encodes a polypeptide of interest linked to the modified luciferase polypeptide, the polypeptide of interest and the modified luciferase polypeptide capable of being expressed as a fusion protein.
 26. A vector comprising the polynucleotide of claim
 1. 27. The vector of claim 26, wherein the polynucleotide is operably linked to a promoter.
 28. A cell comprising the polynucleotide of claim 1 or the vector of claim
 26. 29. A non-human transgenic animal comprising the cell of claim
 28. 30. A non-human transgenic animal comprising the polynucleotide of claim 1 or the vector of claim
 26. 31. A modified luciferase encoded by the polynucleotide of claim
 1. 32. A polypeptide encoded by the polynucleotide of claim
 1. 33. A fusion protein comprising a modified luciferase encoded by the polynucleotide of claim
 1. 34. A method of producing a modified luciferase comprising growing the cell of claim 28 under conditions that permit expression of the modified luciferase.
 35. A method of producing a modified luciferase comprising introducing the vector of claim 26 into a cell under conditions which permit expression of the modified luciferase.
 36. A kit comprising the polynucleotide of claim 1 or the vector of claim
 26. 37. A kit comprising the modified luciferase of claim
 31. 